surge plug pause switch for camcorders...post code return to technomatic ltd. techno house. l468...

THE ELECTRONICS MAGAZINE WITH THE PRACTICAL APPROACIIMarch 1990 UK £1.70

Sinewave inverter

Surge plug

Pause switch for camcorders

Powerline monitor

Temperature compensation

for LCD modules

For fast delivery telephoneyour order on 01-205 9558using VISA Access Card

Orders welcome fromgovernment depts &educational establishments

TECHNOMATICTechno House 468 Church Lane, London NW9 8UF.

Tel: 01-205 9558 Fax: 01-205 0190

rchimedesModelA3000A410/1A42011A44011

Basic Colour"£649£1199£1699£2499

£814ee

SpecialOffer

Ccicur Montor.Carr:age EBIcomputer £12.1system

PHILIPS CM8833 MONITORThe Philips CM8833 monitor offers full stereosound and the possibility of connecting to yourvideo recorder. We can supply this monitor.complete with audio and video leads to connectto A3000 or A400 computers as an alternative forthose who do not have access to a stereoamplifier or Walkman..Add £35 to A3000 colour system price orAdd £135 to A400 colour system prices

TECHNO 410/1Offer extended due to popular demand.Archimedes 410 1 upgraded to full

440 1 spec plusTaxan 770- Multisync Monitorand including The PC Emulator,a packet of discs, a printer lead

and a mouse mat.for only E1999 Carr £12

Finance available on chargeac::: oasis.

TECHNO DTP PackageArchimedes 410 1 Colour Systemupgraded to full 420 1 spec with2 Mb RAM and 20 Mb Hard disc

featuring our technoSCAN packageand either

Acorn DTP PackageFirst Word Plus Rel 2, Logistix

Or

Impression and Pipedream 3and a free mouse mat

for only £1679 carr £12

R140 UNIX SYSTEMLimited Period Offer

R140 Base System

Taxan 770 - or Viking IIplus

Ethernet Card PC Emulatorplus

Administrators Guidefor only

£3000 + VATand it also includes on -site

maintenance contract.

We can provide attractive discounts toEducation Authorities, Schools, Collegesand Health Authorities. Simply phone us orwrite, outlining your requirements. and wewill supply a m uotation.

All prices ex VAT.Prices are subject tochange without notice.Please add carriage(a) £8.00 (Courier)(b) £3.50(c) £2.00(d) E1.50

What we offer in addition to efficientsales service and professional backup!We not only offer professional advice when you are purchasing your system but we will also providefriendly assistance afterwards. We also offer the following incentives to make your purchaseworthwhile.

FREE COLOUR MONITORwith every

400/1 Base System

Special Finance Deal

If you wish, you can purchase the systems listed below at NO EXTRA charge on our retail priceand spread your payments over 13 easily manageable monthly payments. Deposit will be payablewith the order followed by 12 monthly payments. Please phone in with the details of yourrequirements and we will send a detailed offer with the application form for the extended finance.Subject to status, we should be able to despatch your requirements within 48 hours of receipt ofyour order.

Deposit 12 instalments Final Costex VAT inc VAT ex VAT inc VAT ex VAT inc VAT

A3000 £ 65.22 £ 75.00 £ 48.65 £ 55.95 £ 649 £ 746.35A3000 (use with TV) £ 78.26 £ 90.00 £ 51.64 £ 59.39 £ 698 £ 802.70A3000 Colour £ 95.65 £110.00 £ 59.86 £ 68.84 £ 814 £ 936.10A410/1 Colour £139.13 £160.00 £ 88.32 £101.57 £1199 £1378.85A410/1 -,- Taxan 770- £182.61 £210.00 £106.53 £122.50 £1461 £1680.15

ColourTaxan 770-

Techno 4101 systems upgraded to 420 1 Specification£184.22 £211.85 £109.51 £126.00 £1499 £1723.85£247.96 £285.15 £126.09 £145.00 £1761 £2025.15

A440/1 ColourA4401 - Taxan 770+We Eir, credit brokers and can offer credits uoro 24,36 _

£365.22 £420.00 £177.82 £204.49 £2499 £2873.85£417.39 £480.00 £202 22 £232.55 £2689 £3092.35

37,-7_ .7 APR of approx

10% Voucher on Cash & Credit Card SalesCash and credit card purchasers of the above sysTe-- r. =:E .= a voucher to the value of 10% ofthe purchase price. An additional 5% discount v. s. on software purchased with thevoucher. Vouchers will be valid for 90 days from the care of issue.

A versatile hand held scanner for Archimedesoffering four monochrome resolutions (100. 200.300 & 400 dpi) as well as having 4 differentmodes of operation to select gray scaled ormonochrome images.Software is fully integrated with the multi-tasking RISC OS and utilises the desktopenvironment to facilitate easy incorporation ofscanned images into RISC OS compatible DTP.Wp, art or drawing package.The scanning area is 4" wide and vertical heightis limited only by memory constraints. Theimage brightness is adjustable to obtain theoptimum quality. Tone selector allows differentsettings for text and photos.Software appears as an icon on the icon bar fromwhere all its facilities can be accessed. Softwarefeatures include:Visual resealing of either X or Y axis. X & Y flips.colour tinting, picture cropping. on screen help.etc. RISC OS's anti aliaising feature is utilised toenhance the image quality.Scanned images can be saved as sprite file ordragged into other applications. The images canbe output to compatible printer as a sprite usingone of the RISC OS versatile printer drivers.The manual is written in easy to follow style withhints and tips for getting the best results. Themanual together with interactive on -screen helpgets you going almost immediately youhave installed the scanner.technoSCAN complete with interfacecard and manual £149(b)

TECHNOMATIC UPGRADE SPECIALS

Our specially priced upgrades provide aneconomical upgrade path to full 420/1 and 440/1 spec.

1Mb RAM upgrade2Mb RAM upgrade1Mb RAM 20Mb HD3Mb RAM - 20Mb HD31v1b RAM - 40Mb (Toshiba) HD3Mb RAM ÷ 50Mb HD

20Mb HD - Controller (310)HD Controller (3101

E109(c)£215(c)£275(a)£485(a)£689(a)£669(a)£349(a)£179(b)

MONITORSPhilipsCM883314 ColourTaxan 770- 14" MultiSync ColTaxan 770- LIR Low Radiation ColCM1686 16' Hi Res(1280./1024) ColTaxan Viking II 19- Mono

£209(a)£415(a)£449(a)

£1249(a)£849(a)

i-This advertisement can only she... an efl.arnp:e cthe range of products stocked by Tchnomatic. Sosend for our latest BBC catalogue provid,codetailed information and prices on BBC Ci--:_r="Systems. Peripherals. Software and E307..T.,

NAME

ADDRESS

Post Code

Return to Technomatic Ltd. Techno House.L468 Church Lane. London NW9 8TO. agOi

TEL: 01 205 9558

.

I CONTENTS,

March 1990Volume 16Number 176

In the April issueVideo line selector

LEADER \\,'e regret that owing to legalQ meter 11 Compression techniques revolutionize video restrictions we can not pub-Automatic mains switch COMPONENTS

lisp SAVE decoder - Part 2-"RS232 splitterBridge rectifiers revisited

/1 PROJECT: Replacement for TCA280A--as planned. At the same time.supply and design difficulties

Code locking circuit 60 Temperature compensation for LCD modules have made it necessary to

Line allocation tester by M. Clarkson postpone -Sinessave insert-. The multi -MAC chip COMPUTERS & MICROPROCESSORS

er : no new date can as yet be

conceptThe digital model train -final part

31 PROJECT: Plotter Mark IIwith a contribution by B. Lewetz

given for its publication.

Video mixer - final part DESIGN IDEASIntermediate project: testbox 30 Low-cost V/I display module

by Nlohd Abdul Sarni

ELECTROPHONICSFront cover 55 PROJECT: BBD sound effects unitMolecular electronics will beas different to today's elec-tronics as semiconductorsare from the valve technology

by T. Giffard

GENERAL INTEREST.,1/4-._ , -----t

..iimorKi-z---.--- _.-:....::, -

of 40 years ago. This is the 41 PROJECT: Power line monitor

belief of scientists who are by J. Ruffell.. -..--.

_-,s: --

now working on a £20 millionprogramme in Britain. backed

44 PROJECT: Surge suppressorby J. Ruffell

-ii"

iiki-?--_ ,3Aby the Department of TradeMaplin's52 PROJECT: The digital model train - Part 12new distribution centre

and Industry's Link Pro-gramme of collaborativeresearch between universi-ties and industry.

by T. Wigmore

INTERMEDIATE PROJECT

14 Pan 9: IC monitor

p. 18

One familiar example ofmolecular electronics in usetoday is the liquid crystal dis-

by J. Ruffell

RADIO & TELEVISIONplay seen in watches and cal-culators-and even head -up

19 PROJECT: VFO stabilizerby J. Bareford

1.. ..

displays for pilots -thatrespond vigorously to electri-cal or heat signals.Here, scientists at Imperial

20 PROJECT: Interval control for camcordersby Ph. Bosnia

23 PROJECT: Video mixer - Part 3

- -' 9.0* ilwefr-,-- - -

College, London, are working by A. Rigby

on a project to build new 37 Experimental BSB reception

Plotter Mark 11. p. 31types of 'molecular' switchesfor use in waveguides. In the

by R.G. Krijgsman. J.C. Stekelenburg & J. Bulling47 PROJECT: Audio/video modulator

field of conventional electron-ics, electrons flow throughwires and devices like simple

an ELV design

SCIENCE & TECHNOLOGYtransistor switches. In the 50 R & D: keynote of club life at Harwell

-MORRILL Lame*. L;1.Z= ..,- . -1optical equivalent. light tray- by II. Cole. senior scientist at Harwell Laboratory 0 1_ t. i

els down planar opticalwaveguides through 'molecu- TEST & MEASUREMENT -A--.i.O. . -

lar' switches. These switches 36 PROJECT: Digital trigger for oscilloscopescan be made by coating by A. Rigby -.1.16 le...1!glass substrates with a spe- 61 PROJECT: Square -wave generatorcial polymer. In the picture it by NI. Clarksonis being studied with a new -

....technique known as time- MISCELLANEOUS INFORMATIONresolved evanescent wave-induced fluorescence spec-troscopy.

Electronics scene 12 &13: Events 18: Corrections 43;Letters 58: Switchboard 59: Readers services 63: Terms 64:Buyers guide 74: Classified ads 74: Index of advertisers 74

C..) 0

Power line monitor. p. 41

ELEKTOR ELECTRONICS MARCH 1990

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TYPE A' (KSN2036A) 3- round with protective yea*z, bookshelf and medium sized Ht-fi

5c.-c7i.: rs Price £4.90 each + 50p P&P.TYPE 'B' (KSN100SA) 3%," super horn. For generalp_Imcse 57.eakers, disco and PA systems etc. Price£5.99 each 50p PAP.TYPE (KSN6016A)2's5" wide rikspArsron horn. ForqrsaSty Hi-fi systems and quatty discos etc. Price £6.99each -I- 50p P&P_TYPE '13' (HSN1025A) 2'.6- wide asperstort horn.Upper frequency response retained extending down 10rrUd range (210-1z). Strtable for high quality tfr-fl systemsand warty discos Price £9.99 each ÷ SOD P&P.TYPE 'E' (KSN1038A)3I-'x' horn tweeter with attractrre

er finish tr m S:.:lable for HA morutor systems etc.Price £5.99 each + 50p P&P.LEVEL CONTROL Combines on a recessed mountingplate. level control and cabinet input jack socket.85.85mm. Price E3.99 50p P&P.

STEREO DISCO MIXER with 2 x 5 band L & Rgraphs ! s tom 10 sec ment LED.Vu Meters Many outstanding features 5toputsvottl,ndyuat faders pror.rfng a tneful corn -[nation ot the f00orano:-3 lir/Mattes (Map). 3 M'cs 4 Line induct -41g CDplus MIC with talk over switch Headphone Mon -tor. Pan Pot L & R. Master Output controlsOutput 775mV. Sae 360 s280.90mrn. Supp4220-240v,

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jAY lig-4.hI-

B. K. ELECTRONICS Dept EEMESE

Li5.4 UNIT 5, COMET WAY, SOUTHEND-ON-SEA, ESSEX. SS2 6TRTEL: 0702-527572 FAX: 0702-420243

ELEKTOR ELECTRONICS NIARCH 1990

Produced and publishe:: ::, EL EKTORELECTRONICS (Publishing)

Editor/publisher: Len SeymourTechnical Editor: J. ButtingEditorial Offices:Down HouseBroomhill RoadLONDON SW18 4J0EnglandTelephone: 01-877 1688 (National)or +44 1877 1688 (International)Telex: 917003 (LPC G)Fax: 01-874 9153 (National)or +441874 9153 (International)Advertising: PRB Limited3 Wolsetey TerraceCHELTENHAM GL50 1THTelephone: (0242) 510760Fax: (0242) 226626European Offices:Postbus 756190 AB BEEKThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (etekt n1)Fax: +31 4490 70161Managing Director: M.M.J. Landman

Overseas editions:FEDERAL GERMANYElektor Verlag GmbHSOsterfeld Strafle 255100 AachenEditor: E.J.A. KrempelsF,...FFRANCEElektor sariRoute Nationale: Le SeauB.P. 53: 59270 Hailieu]Editors: D.R.S. MeyerG.C.P. RaedersdorfGREECEElektor EPEKariskaki 1416673 Voula - AthenaEditor: E. XanthoulisINDIAElektor Electronics PVT LtdChhotani Building52C, Proctor Road, Grant Road (E)Bombay 400 007Editor: Surervdra lyerNETHERLANDSElektuur BVPeter Treckpoelstraat 2-46191 VK BeekEditor: P.E.L. KersemakersPAKISTANElectro-shop35 Naseem PlazaLasbeila ChawkKarachi 5Editor: Zain AhmedPORTUGALFerreira & Bento Lda.R.D. Estefani. 32-1=1000 LisboaEditor: Jeremias SequeiraSPAINIngelek S.A.Plaza Reptiblica Ecuador2-28016 MadridSWEDENElectronic Press ABBox 550514105 HuddingeEditor: Bill Cedrum

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NDB.Zoeterwoude

Copyright 1990 Elektuur BV

/WC

COMPRESSION TECHNIQUESREVOLUTIONIZE VIDEO SURVEILLANCE

Modern technology has a habit of producing thenecessary equipment to meet the challenge ofthe new requirement. In this case, the primarychallenge is the closer integration of the membercountries of the European Community now lessthan two years ahead.

The technology is that of the state-of-the-artvideoconferencing. designed to make the closerintegration a reality for many officials and busi-nessmen. A front runner in the development ofsuch equipment is GEC Plessey Telecommunica-tions (GPT): GPT Video System products are al-ready in use in organizations and major compa-nies in Europe and other parts of the world.

The European market inte-gration of 1992 may be said tohave been anticipated becausetwo videoconferencing studiosemploying GPT Video Sys-tem's codecs and studio equip-ment were set up in the Euro-pean Parliament in Luxem-bourg and the Commission'sBerlaymont Building in Brus-sels in 1985. The continuingde elopment of video com-pression techniques for thispurpose has meant that manyother applications in video surveillance can nowbenefit from the improved transmission effi-ciency provided by these systems and the conse-quent reduction in system costs.

Efficient data transmission is conditioned bythe amount of information that can be trans-ferred from source to recipient over a link in agiven period without undue analogue network-ing that incurs various delays during the trans-it' issions in the modems used. Secondly, thetransmission of high resolution monochrome orcolour video signals over lone distances ishighly dependent on the bandwidth available andthe degree to which the video signal can be mul-tiplexed with other signals that use the link.

It is important. therefore, that the multiplex-ing efficiency can be optimized within the con-straints of preserving integrity. The employmentof statistical multiplexors. as opposed to time di-vision multiplexors. enables bandwidth utiliza-tion requirements by channels to be reduced ascompression techniques lessen the number ofdata characters to be transmitted.

Data compression methods.The final economy in achieving efficiency isthus to employ video compression to achieve ahigh compression ratio. This involves processingthe source signal so that the information in it isreduced to a form for which the time taken totransmit is minimal, yet the form is such that thesignal can be reconstituted completely to itsoriginal format at the receiving end. There aremany techniques that can be employed in obtain-ing data compression by encoding the signal be -

Video conferencing studios arespringing up all over the world

fore transmission and decoding it on receipt.Examples of these include simplistic methods

such as null suppression, which scans a datastream for repeated blanks or nulls and replacesthem by indicators. Bit mapping is used wherethere is a high proportion of specific types ofcharacter such as numerics and the map indi-cates the presence or absence of characters.

Diatomic coding enables one character torepresent a pair providing a compression ratio of2:1. while an extension of this, pattern substitu-tion. allows a special character code to be substi-tuted for a predefined character pattern. Formsmode operation, used when data from one CRT

is to be transmitted to another.considers some informationfixed. such as a printed format.or variable. such as the data tobe inserted.

There are various other tech-niques of increasing complex-ity for stripping out redundantinformation and reducing whatremains by skilful coding.These have improved over thelast few years. as have the akinmethods of security coding.

In consequence, state-of-the-art encoders and decoders (codecs) necessary formodern transmission networks have achievedconsiderable sophistication. Such is the ingenu-ity of GPT's new range of codecs. the GVS10 se-ries. that, employed in a closed circuit television(CCTV) network, a remarkably high compres-sion ratio can be achieved, resulting in an im-provement in the efficiency of a CCTV analoguesystem by a factor of up to 150.

Flexible codec system.The GVS 10 offers considerable flexibility to theuser and can be configured to take account ofapplication changes and enhancement of the sys-tem employed. Basically. the picture image de-rived from the analogue output of the video cam-era is compressed and digitally coded by the en-coder and then transmitted in real-time to the de-coder, which converts it back to an analogue pic-ture. displayed on a control room monitor.

In this process. the intial signal is memorizedby the encoder so that it becomes necessary totransmit only changes in the picture informationto the encoder.

The value of this feature can be illustratedreadily. In a surveillance role for crowd monitor-ing. where the picture is changing constantly.high transmission speeds and bit transfer ratesare necessary. However, for the remote surveil-lance of premises the incidence of intruder de-tection is hopefully rare and the picture is staticfor long periods. Consequently, a low bit -ratesignal is permissible and signals from a numberof cameras can be multiplexed together. provid-ing a considerable saving in network cost.

ELEK-1 OR ELECTRONICS \ 1 \ RCH 19911

Transmissions can be made at datarates of 2.048 Mbit/s down to 56 kbit/sand a number of encoders can be con-nected to a single decoder. This enables apolling network to be set up with a singlecontrol position in a central spot to moni-tor a number of remote locations. Eachencoder can be configured to provide aunique identity as part of its transmission.so that the decoder can ascertain which lo-cation is being monitored.

In the event of connexion to an unad-dressed decoder, or the loss of videoinput. or a transmission fault, the decodervideo output is blanked automatically. TheGVS series has facilities for local and re-mote diagnostics via a display on the frontpanel. The equipment operation is fail-safe.

EYES DOWN FOR ELECTRONICLIARDICE

The centuries -old five -dice game calledLiardice, which is based on poker and hasmillions of followers around the world,has gone electronic.

Electronic Liardice is a tiny instrumentscarcely larger than a credit card that al-lows the game to be played in placeswhere its traditional wooden or plasticdice would take up too much space or beliable to get lost.

The new version is an interesting ex-ample of the latest gate -array -chip tech-nology that allows chips for specializedapplications to be custom-built by overlay-ing the required interconnex ions on a col-lection of elements on a standard chip. Itoenerates random numbers for the dicefrom reading the internal clock at the in-stant the "roll" button is pressed.

Campus Martius Sales Ltd, Timothy's BridgeHouse, Timothy's Bridge Road, STRATFORD-UPON-AVON CV37 9RN, England.

The new N -channel dual -gate MES-FET TypeCF379 from the Siemens spectrum of GaAs transis-

tors in surface mounting packages is particularlysuitable for input stages in mobile telephones orsatellite receivers. Even at 1.75 GHz it exhibits again of 17 dB with a maximum noise figure of 1.8dB.

(Photograph courtesy of Siemens)

Speeding up decisions.International videoconferencing is becom-ing well established. For example, the lawfirm of Bebner & Company. which spe-cializes in Roman law used in continentalEurope. is planning to provide 40 infor-mal videoconferencing units in Britainwhere businessmen can consult experts inlegal. financial, banking and marketingmatters at videoconferencing centres inother European countries.

December 1988 saw the opening ofCable & Wireless' videoconferencing linkbetween Hong Kong and Singapore. Otherrecent orders for GPT video codecs origi-nate from Italy for Marconi Italia. Japanfor KDD, and Finland for Finnish PTE oilcompany Neste, electronics manufacturersNokia and shipbuilder Wartsila.

11Cfri-71.01\iig 11E'

FREE BOOKLET EXPLAINS NOISE

t\TR Liz

INDUSTRIALNOISE

MEASUREMENJ

The eradication or avoidance of excessivenoise in workplaces has become ofparamount importance to companiesthroughout Europe because of the newregulations that came into effect last Jan-uary. This has created a huge market forsound monitoring equipment. but manybusinesses affected by the new regulationsstill have not the skills or equipment to as-sess noise levels, let alone find solutions.

A simple guide to noise measurementis available from Lucas CEL Instruments.one of Europe's leading manufacturers ofsound monitoring equipment.

The 24 -page booklet covers, amongothers: physical properties of sound; thedecibel and A -weighting scale; the hearingprocess and hearing problems: occupa-tional deafness: and noise induced stress.

Another video link using GPT video -equipment will connect the Royal Bank ofScotland with its Spanish associate BancoSantander. Many international companieshave installed or are installing their owninternal networks to speed the decision -making process. In this context the secu-rity aspect is well covered by crypto en-coders and decoders associated with theGVS10 system.

The fact that compression makes themanagement of a series of locationsspaced over a long distance far more cost-effective has not escaped the attention ofsuch organizations as British Rail. whichis installing GVSIO codecs within a net-work monitoring its unmanned levelcrossings.

Free copies of the booklet are availablefrom Lucas CEL Instruments, 35-37 Bury MeadRoad, HITCHIN SGS 1RT, Phone (04621422411.

DEVICE WILL PREVENT TRAINSPASSLNG RED SIGNALS

British Rail has started work on a newsafety system that will prevent trainspassing red signals. The first pilot schemeis expected to be ready for test commis-sioning later this year.

BR has been planning what it describesas an Automatic Train Protection (ATP)device since 1988 and has recently asked12 firms to bid for the job of producing thefirst of two pilot systems.

UK rail experts say the latest advancesin technology have opened the door to anATP system that will work successfully onthe BR network. which includes some ofthe busiest lines in Europe.

Such a system will work by interactingbetween the signals. the tracks and thetrains, feeding information to a receivingdevice on the train. An on -board computerwill check the information receivedagainst the train's performance characteris-tics and adjust the speed of the train if nec-essar. In this way, the ATP will control atrain's speed if the driver does not do so, inorder that it can always brake in time for ared signal and keep within speed limits.

The first pilot scheme is expected to beinstalled towards the end of this year onlines between London and Aylesbury andBanbury. These lines are currently beingre -signalled and will soon have brand newtrains.

A second pilot scheme will follow onthe main line from London to Bristol.Both systems will be evaluated to estab-lish how a BR network -wide protectionsystem can best be provided.

EL E KTOR ELECTRONICS MARCH 1990

ELECTRONICS SCENE

UK BASE FOR FORD'S EUROELECTRONICS RESEARCH

A new electronics centre set up by Ford ofBritain is claimed to house the most mod-ern test equipment in Europe for automo-tive electronic system. including theworld's most advanced spark plug labora-tory and what is thought to be the largestanechoic chamber for research into caraudio systems.

The £10 million complex forms part ofthe company 's research and developmentcentre at Dunton. It will be the headquar-ters of its European electronics operations.and the focus of electronic systems re-search and development for Ford vehiclesmade throughout Europe.

The centre is working closely withBritish broadcasting oreanizations and theEuropean Broadcasting Union in the de-velopment of radio data systems (RDS)that avoid the need to retune manually tothe strongest signal in different areas, andallows drivers to be given traffic informa-tion automatically.

Carnal is a new secure, frequency hopping, tactical

radio for police and paramilitary forces developed by

Racal Tacticom. It provides up to 2320 channels in

the range 30-97.975 MHz. The set can be pro-grammed to operate in either simplex or two -fre-quency simplex (half -duplex) modes. Controls have

been kept to a minimum for ease of operation and

user convenience. The volume control has asquelch override position which, when selected, indi-

cates the radio's selcal address. Should the radiodevelop a fault, this position will allow a fault code to

be shown in addition to the address.

REAL-TIME COMPRESSION ONINTEL'S VIDEO TECHNOLOGY

Intel Corporation's Princeton Operationhas recently announced a video compres-

sion breakthrough for Technology.giving multimedia application softwaredevelopers and personal computer usersthe ability to compress video footage inreal time, at 30 frames per second (fps), ona personal computer. The ability to com-press motion video in real time, a symmet-rical process, and to play it back immedi-ately at full speed and on the full screen ofa computer. is now possible through theDVI software advance known as RTV (forreal time video). version 1.5.

Bridging the gap between the best of Bruel & Kjaer's

sound level meters and the company's top -of -the -

range laboratory real -lime signal analyser is the new

Type 2143 Real-time Frequency Analyser illustrated

here. It provides analysis down to 1124 octave, inreal time, in the field. Large internal memory plusdisk storage allow for storage of set-ups and refer-

ence data for field use. The 2143 weighs less than

10 kg and its battery life is not less than lour hours.

COMPUTER GUIDES EMERGENCYSERVICES

An advanced computer system designedby Marconi Command and Control Sys-tems helps fire brigades, civil defence au-thorities and other emergency services toeffectively manage action and resources.

MACE (Mobilization and CommandEquipment) interfaces with normal radiocommunications systems, the public tele-phone network, or any other communica-tions network. In addition to continuouslyupdating the current holdings and status ofequipment at every station in the opera-tional area, the system also holds specialistdatabases, such as information on haz-ardous chemicals and explosives. It canalso provide pre -determined response lev-els for every building or type of incident,further aiding resource management.

SHOOTING STARS FORTRINITY HOUSE

Sending messages by shooting stars andnavigational buoys powered by wind andsea are among new marine aids currentlybeing evaluated by Britain's Corporationof Trinity House (TH), one of the world'soldest maritime organizations.

Much has changed since King HenryVIII empowered Trinity House to erectbeacons to safeguard English ships andtheir sailors. Communication techniqueshave become increasingly sophisticatedand the role of Trinity House reflects this.Of the 85 lighthouses it now operates inEngland, Wales, and the Channel Islands(Scotland has its own maritime organiza-tion), 60 have been automated and the re-mainder will all be unmanned by the endof the century. In the past year the last ofthe corporation's 13 light vessels switchedto total automation, while of its 400 buoysmany are solar powered today.

One technique currently undergoing atwo-year trial is the exploitation of shoot-ing stars, or meteor -burst communication.From the manned Rona Lighthouse, 56 kmnorth of Scotland, Trinity House is bounc-ing digitized data to monitor and pro-gramme unmanned lighthouses, light shipsand buoys.

Computer equipment monitors shoot-ing stars and uses their trails to transmitinformation during the split second theyflash through the sky. The relatively lowcost and long range of meteor burst sys-tems offer great advantages over conven-tional forms of radio and satellite commu-nication.

Meteor bursts-vast numbers of mete-ors streak through the earth's atmosphereevery day-leave a white hot trail whenthey hurtle towards the planet at speeds ofup to 72 km/s. The cosmic projectiles arevaporized by the friction caused by theircontact with the air, and the air torn apartby their entry into the atmosphere forms ashort-lived trail of ions.

The technique has already been used togain knowledge of weather conditions andbreakage in Alaskan pipelines.

New from Flight Electronics is the FLT -32 trainingsystem. Based on the industry standard 8030/8050series of microcontroflers, the FLT -32 is designed to

teach students a wide variety of industrial control ap-

plications. The system comes with everything you

need to get started, including power supply andcable to connect the system to a terminal or a PCrunning terminal emulation software. Details from

Flight Electronics, Ascupart House, SOUTHAMP-

TON SO1 1LU, Telephone (0703) 227721.


14

INTERMEDIATE PROJECTA series of projects for the not -so -experienced constructor. Although each article

will describe in detail the operation, use, construction and, where relevant, theunderlying theory of the project, constructors will, none the less, require an

elementary knowledge of electronic engineering. Each project in the series will bebased on inexpensive and commonly available parts.

9. IC MONITOR

J. Ruffell

Digital probes come in many shapes and versions. All of these,however, suffer from a single disadvantage: they can monitor thelogic level at only one IC pin at a time. To overcome this limitation,

we propose a 16 -way IC monitor with a probe that can be clipped onto virtually any commonly used logic dual -in -line integrated circuit

with up to 16 pins. Ideal for getting to grips with digital circuits, thisIC monitor gives an instant indication of all input and output levels

simultaneously. Interestingly, it automatically finds the power pins ofthe IC under test and works with most TTL and CMOS circuits.

The circuit of the IC monitor (Fig. 1) con-sists of 16 identical smaller circuitspowered by one supply. The operation ofthe input circuits will be described withreference to the top one, which consists ofDr-Dis-Ris-No-R2-116.

The IC monitor is powered by the cir-cuit under test via the two supply pins ofthe IC it is connected to. This means thatthe power supply of the circuit under testmust be capable of supplying an addi-tional current of up to 500 mA to powerthe IC monitor. Make sure this is the casebefore connecting the monitor!

You are probably aware that pin 14 of14 -way DIL logic ICs is usually the posi-tive supply terminal, and pin 7 theground terminal. For 16 -way ICs, the re-spective pins are usually 16 and 8. Unfor-tunately, there are also many ICs whichdeviate from this rule of thumb -theirpower connections are at pins other than14 or 16, and 7 or 8. The IC monitor, how-ever, finds the power pins automatically.How? Let's examine the input circuit alittle closer.

If a valid logic level is measured atpin 2 of connector Ki, it will be either a 1or a 0. Whichever, the absolute voltage isinvariably a little lower (for a 1) than thepositive supply voltage, or a little higher(for a 0) than 0 V. This is because theswing of logic IC outputs is nearly alwayssmaller than their supply voltage owingto the forward drop across the output

transistor(s). Invariably, only two of thediodes D1.-D4s will therefore conduct andpass the supply current because they arethe ones connected to the highest poten-tial -the supply voltage.

On the above assumption that pin 2 ofKi carries a logic level and not the positiveor negative supply voltage, diodes ftand D17 block, but the monitor circuit ispowered by two other diodes. The logiclevel is applied to the input of inverter N-

0.1

via series resistor Res. Depending on themeasured logic level, the inverter sup-plies either a low output level (input =high), or a high output level (input = low).Hence, the LED at its output, D16, lightsonly if the measured level is high (1).

TTL and CMOS

There are a large number of significantdifferences between ICs from the TTL


IC MONITOR

(transistor -transistor logic) and the CMOS(complementary metal -oxide silicon) fam-ily. The most important difference is thesupply voltage range of about 4.5-5.25 Vfor TTL circuits against about 3-18 V formost CMOS ICs (note: there are many ex-ceptions to this rule).

Since the IC monitor is to be suitablefor use with TTL as well as CMOS ICs, itwould appear logical to use CMOS inver-ters from the well-known CD4000 series,since these have the larger supply voltagerange. Unfortunately, the outputs of theseICs can not sink enough current to drive aLED direct. The alternative, 16 discretecurrent amplifiers, must be rejected be-cause it would require a quite complexcircuit. There is, however, an IC familycapable of working at relatively low sup-ply voltages and sinking the current re-quired to light a LED: the 74HC series.

The one disadvantage of the 74HCseries, the maximum supply voltage ofabout 6 V, is fairly simple to overcome byusing a series regulator which limits thesupply voltage taken from the circuitunder test to a value which is safe for theinverters in the IC monitor. This regulatoris a discrete circuit, Rsi-DscI-T2. Before itslimiting action starts, the output voltageof the series regulator follows the inputvoltage quite accurately, which is an im-portant requirement for 5-V digital sys-tems.

Circuit Ti-Rso-D-19 forms a voltagesource which limits the LED current(s) toan acceptable level at relatively high sup-ply voltages. Let's assume that the circuitunder test works at a supply voltage of12 V, and that the voltages across Dr and

are about 2 V. Without Ti, the seriesresistor for the LED would have to dropabout 10 V. Similarly, for a system opera-ting at 5 V, the drop would work out atabout 3 V, which evidently requires an-other resistor value. The solution to thisproblem has been found in the use ofseries resistance, Ti, whose value in-creases automatically with the supplyvoltage. Since Ti limits the LED voltage toabout 2 V, a single resistor value (22 S2)may be used for the full range of the sup-ply voltage.

Open input?In general, inputs of CMOS ICs mustnever be left open. You may have foundout already from experiments that anopen (non -connected) CMOS input causesthe IC to heat up and destroy itself rapid-ly. The actual destruction is normallycaused by excessive current drawn by theoutput stages. Obviously, this effect mustbe avoided at all times and calls for anadditional function of the IC monitor: de-tection of open CMOS inputs.

The circuit to do so is an oscillator,NI, -N16 -R17 -Pi -Co. When switched onwith Si, it supplies alternating low andhigh levels to the inverter gates via2.2 MS2 resistors. When the oscillator isswitched off, these resistors ensure well-defined low levels at the inverter inputs

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that do not receive a logic signal from thecircuit under test. The high resistor valueof 2.2 MC/ ensures at the same time thatmeasured signals do not see an additionalload, so that the inverters can follow thehigh and low levels reliably.

Finally, note the type of diode in posi-tions DI7-D-is: the 1N4151 is used ratherthan the perhaps more familiar 1N4148because of its lower forward voltage drop,which is essential for correct operation ofthe circuit.

ConstructionSince the circuit is quite complex by thestandards used in this series of articles, itis best to build the IC monitor on theprinted -circuit board shown in Fig. 2. Thisboard is available ready-made throughthe Readers Services. For those with ac-cess to a photographic dark -room and the

necessary etching and drilling equipment,the mirror image of the track side of thecircuit board is shown to enable a trans-parent film to be made from a photocopy.

Since the pad density is fairly high inplaces, the PCB must be soldered withgreat care and precision. Work accuratelyand use a low -power iron and little solderto prevent short-circuits between adjacenttracks and pads.

Start the population with the wirelinks. Next, fit the passive parts (capaci-tors, resistors, IC sockets, the preset andthe pin header). Lastly, mount the transis-tors and the diodes (but not the LEDs),taking good care to maintain the correctori en ta tion.

The power transistor, T2, is fitted witha small U-shaped heat -sink (TO -220 style)to assist in its cooling. The heat -sink isbolted on to the board together with thetransistor. An insulating washer is not re-


16 INTERMEDIATE PROJECT

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quired. Be sure to leave the terminals ofthe BD175 long enough so that they can bebent at right angles for inserting into thePCB holes without touching the heat -sink.

Next, mount each LED such that thelower side of its plastic body is about levelwith the top of the heat -sink. Do not fit thecompleted PCB into the enclosure as yet.

Initial testUse a pair of light -duty flexible test leadswith small crocodile clips to connect a DCpower supply of 5-18 V to any two pins ofconnector Ki. Set Pi to the centre of itstravel. Set switch Si to position B (inverterinputs logic low). If the circuit works sofar, the LED associated with the pin con-nected to the positive supply voltage willlight. Set Si to position A (oscillator on)and check that 14 LEDs flash. Adjust Pt forthe required flash rate. Next, systemati-cally connect the positive and negative

COMPONENTS LIST

Resistors:= 2211

R17 = 220kflis;R2o;Rn;R24;R25;R26;R:R32;R34;R36;R3s;R4o;1142:R44;R46;Res = 100k

Ris;R21;R4.:1,325;R27;R2e;R3i;R33;R35;R37;1339;R41;1143;Ft45-.R47:R49 = 2M2

Rso = 2200. 1 WRst = 6800Pt = 'IMO preset H

Capacitors:Ct = 1011;25 VC2 = I nO

C3;G4;Cs =10nCO = 470n

Semiconductors:DI-Dte = LED; red: 5 -mm dia.1317-1345 = 1N-1151

D49 = 2V7; 400 mW zener diode050 = 6V8: 400 mW zener diodeIC I ;IC2:1Co = 74HC1 4Ti = BD175T2 = BC337

Miscellaneous:Si = miniature toggle switch.Kt = 16 -way angled pin header for PCBmounting.K2 = 16 -way IDC socket.K3 = 16 -way IC test clip (e.g.. ElectroMailstock number 423-627).TO -220 or TO -126 style heat -sink.Approx. 50 cm 16 -way flatcable.PCB Type 896140 (see Readers ServicesPage).


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supply wires to all other inputs to veri:vthe operation of the associated diodes(e.g., pair Di:-Dis for Ki pin 2).

Case and test cableThe completed, tested and adjustedprinted -circuit board is fitted in a suitablysized ABS enclosure, for which a sug-gested front -panel lay -out is given inFig. 5 (ready-made front panel adhesivesare not available). Cut a rectangular slotin one of the short sides of the enclosureto enable an 1DC (insulation displacementconnector) to be connected to Ki.

The construction of the 16 -way flat -cable between the IC monitor and the testclip is illustrated in Fig. 4. Contrary towhat many electronics retailers and con-nector manufacturers would have you be-lieve, an IDC is fairly simple to fit on to aflatcable of almost any width, without theuse of special (very expensive) tools.

Cut the cable as straight as you canusing a large pair of scissors. Insert it be-tween the socket (or header) and the asso-ciated cap, taking care to align theindividual wires in the cable with the V-shaped clamps which are to receive them.Note the position of pin 1 on the connec-tor, which is usually marked. Make surethis pin is at the side of the single colouredwire in the flatcable.

Most IDCs have a U-shaped cap withsnap -in fittings on the side guides, whichreadily lock with the main connector.Carefully place the cap on the socket,pressing it down with equal force at bothextremes to prevent one guide locking be-fore it is due. Use hand force to clamp thehateable between the socket and the cap.Check whether the hateable and thesocket are at right angles. Next, use a

Fig. 4. The test cable is made from an IDC. a length of flatcable and a 16 -way IC test clip.

small piece of wood and a light hammer,or a carefully operated vise, to press thecap further on to the socket until the partsclick together. Apply a little more force toensure a good connection. Some IDCshave an additional cap that functions as astrain relief. Fold the flatcable back and fitthis second cap.

Connect the pins of the 16 -way IC testclip to the corresponding wires at theother side of the flatcable. Be sure to con-nect the hateable wires to the same pinnumbers as Ki (Ki pin 1 goes to test clippin 1, etc.). Finally, use an ohmmeter or acontinuity tester to check whether all con-nections are in accordance with the circuitdiagram.

Practical useNo doubt you will soon find the IC moni-tor an indispensable and easy -to -use testinstrument for a wide variety of digitalcircuits. Open inputs are traced rapidly byswitching Si to the oscillator position. Anyone LED which starts to flash in additionto already flashing ones indicates an openinput (remember that slowly changinglogic levels applied to the IC may causeLEDs to flash if the oscillator is switchedoff with Si). If the frequency of a measuredlogic level exceeds about 25 Hz, the rele-vant LED no longer flashes, but appearsto light at reduced intensity. Finally, makea habit of switching off the circuit undertest before placing the clip on an IC.

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WIAP_IN OPENS NEW S2 MILLION DISTRIBUTION CENTREAs part of its planned expansion campaign andstill remain able to honour its pledge to cus-tomers for a same -day mail -out service.Maplin Electronics PLC has recently,' opened anew £2 million distribution centre at Womb-well. Barnsley.

Local MP Terry Patchett unveiled a com-memorative plaque in the presence of a gather-ing of directors. staff, local suppliers andmembers of the local and trade press.

For directors Roger and Sandra Allen. andDoug Simmons. it was a milestone on the roadto further success for a business that began asa part-time venture in the back bedroom of ahouse in Essex in 1972.

Roger Allen, the managing director, toldElektor Electronics: "We began by making upkits. but we had such difficulty in securingcomponents that we decided to go into thebusiness of supplying electronic components".

With its dedication to its customers, theMaplin business has grown to such an extentthat h is currently handling over 13,000 ordersa week with an average order value of £18.00.Hence the need for this purpose-built distribu-tion centre.

The new 95,000 sq.ft. centre, which standson a five -acre site. has been created to ensurethat orders are dealt with on a same -day dis-patch basis. The centre is a vast Aladdin's caveof electronic items. from the smallest compo-nent to complete,electronic equipment.

Incoming mail orders are dealt v. ith at thehead office in Hadleigh. Essex. and these, aswell as telephone order,. are processed withthe aid of comprehensive computer programswritten entirely within the company. Dispatchdetails are sent immediately in data form overprivate circuits to the new distribution centre

IEE MEETINGS5-8 Mar - Digital communications.8-9 Mar - Safety related control systems.18-23 Mar - Digital signal processing

devices and applications.19-22 Mar - UK IT.25-30 Mar - Network technology.

Information on these, and many other. eventsmay be obtained from the IEE, Savoy Place,LONDON WC2R OBL, Telephone 01-24-1871.

The SI Semiconductor International andINTERNEPCON will take place concur-rently from 20 to 22 March at the NationalExhibition Centre. Birmingham. Details fromthe organizers Reed Exhibition CompaniesLtd, Oriel House, 26, The Quadrant,RICHMOND TW9 IDL, Telephone 01-948 9900.

where they arc printed and prepared for dispatch to the customer- all in one day!

Details of over 300.000 customers whohave bought from Maplin over the past threeyears are held on a computer data -base andthese customers are mailed twice a year withinformation of new items.

In the October mail -shot, customers are en-couraged to purchase the annual cataloguewhich has complete information on the totalrange of 7,000 stock lines. The catalogue maybe bought by mail-order or from any branch ofW H Smith, who account for the distributionof about 130,000 out of the 200.000 cataloguessold.

Eighty per cent of Maplin's turnover comesfrom private individuals who are purchasingfor their hobby. Maplin publishes a bi-monthlymagazine that gives technical information andconstructional details of a number of projects.

The company now has 11 retail shops inmajor towns and cities, including London.Bristol, Manchester. Birmingham. Leeds. Not-

A five-day course on direct broadcast satel-lite television is being organized jointly byERA Technology and Professor B.G. Evansof the University of Surrey. It will take placefrom 26 to 30 March at the University inGuildford and is intended to provide dele-gates with a sound technical background insatellite TV and supporting technologies. aswell as the commercial insight to take full ad-vantage of current and developing businessopportunities. Details from ERA TechnologyLtd, Cleev Road, LEATHERHEAD KT227SA. Telephone (0372) 374151.

The Financial Times eighth conference onTelevision and Satellite Broadcasting.which will be held in London on 28 Februaryand 1 March. coincides with a crucial turning

tingham, Southampton. Westcliffe. Newcastleand Reading.

From the customer records built up on thecomputer, Maplin has been able to identify 19more areas in the country where Maplin shopscould be sited and it is planned to have a totalof 30 shops operational by the end of 1993.

A very small proportion of the ready-mademodules that are for sale are manufactured byMaplin using out -workers, but the vast major-ity of the product range comes from manufac-turers in the UK and abroad.

Because of the very wide range of stocklines. the company buys from numerous sup-pliers. most of whom are in the UK (some500) but some (about 25) in the Far East.

The main Maplin computer, based atHadleigh, is equipped to process 90 orders si-multaneously: it has 675 Mbytes of on-linedisk storage. This is used for order processing.supplies to the shops, stock control and pur-chasing. A smaller, 32 -line, computer servesthe distribution process at Wombwell. Stockorders from the shops are received in dataform via the telephone and a complete Elec-tronic Point of Sale system is being designed.

All the Maplin computer software has beenconverted to run under the operating systemnamed PICK and this, apart from being an idealsystem for commercial use, also has the advan-tage of allowing a range of hardware beingused without the necessity of alterations to thesoftware.

Apart from expansion in the UK. Maplinintend to penetrate more deeply into continen-tal European countries and so be able to selldirect to greater numbers of individual cus-tomers there by early 1992.

point for the media industries, both in the UKand in the rest of Europe. One year into thedirect -to -home satellite revolution in Europe,top speakers will be examining the implica-tions of Britain's legislative moves towardsderegulating broadcasting and the creation ofnew channels. the scheduled launch of BritishSatellite Broadcasting and the impact of asecond Astra satellite. Details from FinancialTimes Conference Organization, 126Jermyn Street, LONDON SWIY 4UJ,Telephone 01-925 2323.

The Digital Cordless Communications con-ference, to be held at the Meridian Hotel.London on 12 March. and the Open Systems& Interoperability conference to be held atthe QED Centre, Westminster, London from26 to 29 March. are organized by BlenheimOnline Ltd. Blenheim House, Ash HillDrive, PINNER HAS 2AE, Telephone 01-868 4466.


19

VFO STABILIZERThe stabilizer presented here enables theprecise tuning of HF oscillators for up to100 MHz if these have a frequency controlinput. That input is normally used for va-rying the capacitance of a varactor.The signal at the input of the circuit isamplified by a fast operational amplifier,ICi. The output of this opamp is a rectan-gular signal that is applied to the D (data)input of bistable FF1. The clock input ofthe bistable is provided by generator IC,The two outputs of the bistable are theproduct of the clock and the input signal.The frequency of this composite signal liesbetween 0 Hz and half the clock fre-quency. To ensure the best possible con-trol characteristic, the output signal of thebistable is compared with a reference sig-nal that has a frequency one quarter of theclock. To that end, a second bistable, FF2,is connected as a binary scaler; its input isprovided with a signal whose frequencyis half that of the clock applied to FFi.

The differentiating network at the out-put of FF1 uses only the negative pulses ofthe output signal, whereas that at the out-put of FF2 uses only the positive pulses.All these pulses are combined in an inte-grator, resulting in a stable control volt-age. Since both the Q and the Q output areused, the ripple is halved.

If the frequency of the input signal isnot stable, the amplitude of the integratedsignal varies. The variations are used tocontrol the oscillator in a manner wherethe deviations are negated.

The clock is constructed around aCD4060 and an inexpensive watch crystal.The crystal may, of course, be replaced by

a different type, as long as this has therequired stability.

The clock frequency, and thus the re-quired grid, is set with the aid of jumpleads. The frequency on row B must al-ways be half that on row A.

The construction and alignmentshould not present any undue problems ifthe circuit is built on the PCB shownbelow. The oscillator is set to exactly itscentre frequency by 0,1: this can be veri-fied at test point TP, which carries thebuffered clock frequency.

The circuit is powered by a 12-V sup-ply that is brought down to 5 V and stabi-lized by regulator ICF..

Indicator D6 remains out as long aslong as the oscillator frequency is stable

If the frequency drifts, the 1ED lights, itscolour and intensity indicate in what di-rection drift occurs and how serious thedrift is.

The integrating action may be disabledby Si, which allows the circuit to settledown more rapidly than with it on.

COMPONENTS LIST

Resistors:3 1k

1 10k

1 2k26 1M01 10M1 220k2 68052

Capacitors:1 22n ceramic1 411716V1 100nF ceramic1 lOnF ceramic4 470pF polystyrene1 60pF trimmer1 33pF1 68pF2 1110 MKT

2 47pF 16V1 100nF MKT

Semiconductors:5 1N41481 bicolour LED1 uA733

R2

R:?

R3

F19.

R14;R:5

CIC2

C3

C4

Cs-CaCsCisCI I

Cl2;CI3CIS:C15

C17

DI-D5D6

ICI1 74F74 or 74S74 or 74AS741 CD4060 IC31 LF411 IC4

1 78L05 ICs

Miscellaneous:1 SPBT switch1 crystal 32.768 kHz1 PCB

1C2

894023


CON,CAMCO

Philip Bosma

TUOL P'ORS

Prices of camcorders have shown a welcome reduction over the last year or so, andan increasing number of enthusiasts are using these successors to the 8 -mm and

16 -mm film camera. The circuit described here is an accessory that allowsrecordings to made of events that take a relatively long time. The opening of a

flower, for instance, can be filmed at regular intervals and then played back in a fewseconds.

The recording principle of the camcorderis basically the same as that of a filmcamera: a series of individual pictures iscaptured and subsequently played back toreproduce the original visual impress-ions. The camera of a camcorder has arange of shutter speeds, in economy mod-els ranging from te:io to 1/1000 and in themore luxury models from 1/50 to 1/4ocio.

Short shutter times allow the user to makerecordings of relatively fast events as theyoccur in, for instance, sports. By contrast,long shutter times are required to ensuresufficient intensity of incident light on therecording element, which is usually aCCD (charge -coupled device). As in filmcameras, these shutter speeds are not suit-able for slow-motion filming, which there-fore requires a different approach.

The usual method is to make short rec-ordings at regular, adjustable, intervals.When these recordings are played back atthe normal speed, the relatively slowevent is reproduced at a much faster rate.In this manner, a slow event with gradualchange that takes, for instance, an hour,may be shown in a few minutes or even afew seconds.

The circuit described here is switchedon automatically during a predefinedperiod of time. After each recording peri-od, the camcorder is switched back to thestand-by state, the length of which is alsodefined by the user. The circuit effectivelydisables the interval switch (or pauseswitch) in the camcorder. This switch isusually of little use and offers a fairlycrude control.

Practical use of the control is simple: fitthe camera on a tripod or mount it on atable, aim and focus it on the flower, andswitch on the interval control. After halfan hour, or an hour, or even longer, de-pending on the flower, a perfect recordinghas been made of the flower opening.

The circuitThe circuit diagram shown in Fig. I couldhardly be simpler. Note that only one ICis used, and that about half the circuitserves no other purpose than the control

Fig. 1. Circuit diagram of the interval control, which is basically an astable multivibratorwith adjustable on and off times.

of an indicator LED. The result is a smallcircuit board for which a compact enclo-sure should be easy to find. A single 9-VPP3-size battery is used to power the in-terval switch. Since the circuit consumeslittle power, the battery should offer suf-

ficient capacity for extended periods ofoperation.

The interval control is basically an as-table multivibrator with adjustable fre-quency and duty ratio. Resistors RI, R2and R4 determine the voltage at the non-


INTERVAL CONTROL FOR CAMCORDERS

inverting input of opamp Ai. Because offeedback resistor R4, the voltage at thenon -inverting opamp input is either V4 or3/4 of the supply voltage, depending on theoutput voltage of the opamp. The hys-teresis so created in the switching beha-viour of the opamp causes it to function asa kind of Schmitt -trigger. The R -C combi-nation between the inverting input andthe output of the opamp extends this func-tion to that of a multivibrator.

The opamp output is high if the voltageacross Ci is lower than 0.25Ub. The timeneeded to charge CI from the low triggerthreshold, 0.25Ub, to the high trigger thre-shold, 0.75Ub, is determined by preset P2and potentiometer P4. The total resistanceset with P2 and Pi is in direct proportionto the time the opamp output remainshigh. When the voltage across Ci exceedsthe high threshold level, the opamp out-put goes low. As a result, Ci dischargesuntil the lower trigger threshold isreached. Diodes Di and D2 allow differenttimes to be set for the charging and dis-charging of CI.

Transistor T: conducts as long as theopamp output is high. In this condition,the remote control inputs of the cam-corder are connected via MOSFET T: sothat the recording function is switched on.This lasts until Ci has discharged to thelower threshold level, when the opamptoggles and T2 is switched off.

The component values in the mutivi-brator allow maximum recording -on and

-off times of about 400 s to beset. A minimum setting is provided bypreset Pi to ensure that the camcorder hassufficient time to produce a synchronizedpicture. This minimum recording intervalis called the backspace time and is sped-fied in the user manual with most cam-corders. If the backspace time is notknown, it is fairly simple to establish froma few experiments.

The second part of the circuit is therecording -on indicator set up aroundopamp A2. This is configured as an astablemultivibrator of which the duty factor andoutput frequency are fixed. It is started themoment At supplies a high level. DiodeDi causes the on -time of A2 to be muchshorter than the off -time so that LED D3flashes. This is done to reduce the averagecurrent consumption of the circuit toabout 3 mA whilst ensuring a clear indi-cation that a recording is being made.

Building the controlFigure 2 shows the component mountingplan and the mirror image of the track sideof the small PCB. Construction of the cir-cuit is straightforward. Start by fitting thesolder pins, followed by the resistors,presets and capacitors. Next, mount thediodes, the integrated circuit and the tran-sistors. Use little solder and work accur-ately.

Potentiometers 132 and Pi are either sol-dered direct to the board, or connected toit via short lengths of insulated wire.

Finally, fit the circuit into a small ABS

enclosure with a battery compartment.The timing controls, the on /off switch andthe indicator LED should be fitted on thetop panel for easy access.

The interval control is connected to thecamcorder by a short length of 2 -wirecable. A 3.5 mm jack plug is used at theside of the interval control, and a 3- or5 -pin DIN plug at the side of the cam-corder.

COMPONENTS LIST

Resistors:5 1M0

1 4k71 560k1 3M31 47k1 150f.2

2 50k preset H2 2M5 lin. potentiometer

Capacitors:220u 16V

1 1p0 16V1 100n1 10u 16 V

Semiconductors:3 1N41481 LED1 BC54781 BS1701 TL082

Miscellaneous:1 3.5 mm jack socket1 miniature SPST switch1 PCB

RI:R2;195:Re4R-

R3

R4

Re

FITf

P:P2Pa:P-i

CCcC3

D:D2:D2D-!

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K1

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ra

otR7 Eo

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0

O

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o

0-0 -

0-

Fig. 2. Single -sided printed circuit boardfor the interval control. The time controls. Psand P4. may be soldered direct to the board.


REPLACEThe "Computer -controlled slide fader" wepublished in 1988 (Ref. 1) was based ondimmer chip Type TCA280A. In spite ofthis device being a Philips Componentspreferred product at the time, it proveddifficult to obtain for many readers. Whenapproached, Philips Components ad-mitted that they had taken the TCA280Aout of production without prior warning,and that no pin -compatible replacementwas available.

It has taken us some time to find asuitable replacement and have found thatthe Type TCA785 from Siemens is a good,but not pin -compatible, substitute, whichalso required some redesigning of theoriginal circuit. The result is shown in thecircuit diagram, Fig. 1.

The VSYNC input is provided with a50 Hz square wave, which is used inter-nally for mains synchronization. The IC ispowered via R:, D3, Ci and zener diode D4.

An internal current source, set by Piand Rs, causes a linearly rising voltage onC3. At each zero crossing of the mainsvoltage, Cl is discharged rapidly, so thatthe potential across it has a sawtoothwaveform. The amplitude depends on thesetting of Pi.

The sawtooth voltage is comparedwith a control voltage that is applied topin 11 of ICI via filter Rs -C2. If the saw -tooth voltage rises above the control volt-age, a pulse is generated at pin 14 or 15,depending on the current half cycle (posi-tive or negative) of the mains voltage. Thetwo outputs are connected to a triac viadiodes D5-11 and resistor Re, which en-able the triac to be triggered. The instant

COMPONENTS LIST

Resistors:Ri = 27kR2 = 3302R3 = 2k2Ra = 10kRs;R7= 4k7Rs = 150

= 100k preset HP2 = 10k linear potentiometer

Capacitors:= 470g; 25 V (fitted at track side)

C2;C3 = 100nC4=150p

Semiconductors:ICI = TCA785 (Siemens: ElectroValue Ltd.)Tn.+ = T1C236 or T1C246Di;Dz;Ds:Ds = 1N4148

Da = 1N4001D4 = zener diode 15 V; 1 W

Miscellaneous:Si = miniature SPST switch.PCB Type 894078 (see Readers Servicespage).

TCA280A

Fig. 1. Circuit diagram of the TCA785-based lamp dimmer circuit.

that the triac begins to conduct is, there-fore, dependent on the control voltage atpin 11, resulting in a voltage -controlleddimmer. The control voltage may be pro-vided by the slide projector or a poten-tiometer. In the latter case only, it is alsopossible to dim 12-V halogen lamps.Zener diode D4 then needs to be replacedby an 8.2 V type.

The dimmer is aligned by adjusting Piin the off condition, when the control volt-age is at a maximum, until the lamp justglows.

The slide projector is aligned by settingthe relevant potentiometer on the projec-tor PCB to the centre of its travel, when thelamp(s) should be out.

When that is done, the lamp(s) shouldbe switched on and off a couple of times

to make sure that the two potentiometers(Pi and that on the projector board) areadjusted correctly.

Since the control characteristic of theTCA785 is different from that of theTCA280A, it is not advisable to mix thetwo devices.

When Si in the present dimmer isclosed, the projector lamps are off: inother words, for normal operation, Simust remain open and it may, therefore,be omitted in some cases.

Reference:

1. "Computer -controlled slide fader"Elektor Electronics March 1988 and April1988.

Fig. 2. The printed -circuit board may be used for four lamp dimmer circuits.

Et.EKTOR ELECTRONICS MARCH 1990

VIDEO MIXER

PART 3: KEYBOARD

A. Rigby & G. Dam

This penultimate instalment discusses the third module in the videomixer: the keyboard with its many switches and controls for picture

mixing and special wipe effects.

The keyboard circuit forms the user inter-face of the video mixer. The block diagramin Fig. 11 shows the general structure.Each of the switches shown in a horizontalTOW roughly at the centre of the diagramhas its own LED indicator. The switchstates are demultiplexed to give two or, insome cases, four independent control sig-nals. The diagram also shows that the out-put signals of switches S5-Si: and S3:'-535are synchronized to the YSYNC signal. Thismeans that any action on the keyboarddoes not take effect until the vslNc pulseis generated in the mixer. Thesynchronization eliminates unexpectedswitching effects occurring at random in-stants during the current raster.

The lower part of the block diagramcontains an EPROM plus associated logiccontrol circuits. The loading of state levelssupplied by switches S1-S4 and S14-S24 issynchronized by VSYNC to ensure that theeffect associated with a particular switchbecomes visible at the start of a new rasteronly.

After buffering, EPROM datelines DO-D5 are used direct in the mixer. DatalinesD6 and D7, however, are first applied to a1 -of -4 decoder to give the required controlsignals SC15-SC18. The combination ofcontrol lines MCI-MC6 and buffered da-talines DO-D3 provides a total of 64 differ-ent combinations, or 256 combinations ifSC15-SC18 are added. Each combinationrepresents a particular picture wipe ormixing effect.

OUT

SCI.SCA

SELECT1 OF 4

SS S8

LEDINDIC.

VSYNC

VSWHSYNC

HSW

PREVIEW

sc.4.scs

SELECT1 OF 4

59 -512

LEDINDIC.

VERTICALSWITCHING

EPROM

BUFFER

SIMP

SELECT1 OF 2

S30 -S31

LED

BLOCKSELECT

A4

04 07

SELECT10F4

5:15 -Eta

EFFECT

SEL till

SELECT1 OF 2

S32

LEDINDIC.

SELECT1 OF 4

SELECT1 OF 16

keylock

513

SEL ItiillSCI2,5,7.1!

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534.535

LED

S1- S4

H MODV MODW.77, MA

4

SELECT1 OF 2

535 537

LEDINDIC.

LEDINDIC.

41514.529 1 LEDINDIC.

57) 4.55.

Fig. 11. Block diagram of the keyboard unit.


24 RADIO AND TELEVISION

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ELEKTOR ELECTRONICS NIARCH 1990

VIDEO MIXER PART 3: KEYBOARD

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RADIO AND TELEVISION

Clearly, a total of 256 possible combi-nations results in an unwieldy number ofeffects. Therefore, a selection has beenmade on the basis of practical use. Ob-viously, this selection is subjective, but theuser of the mixer is free to design and storehis own set of effects, as discussed later.

In the basic version of the mixer, theEPROM contains only one of 16 possiblebanks of picture effects -up to 15 may beadded as required. The effects obtainedfrom the above selection are stored in thefirst bank of the EPROM, and may becalled up by a total of 20 keys. The firstkeyboard area consists of 16 keys, 814-529;while the second area consists of fourkeys, Si -84. The latter allows the user toselect one of four effects offered by onekey from the first (20 -key) area. If you findthis difficult to follow, look at the front -panel lay -out (Fig. 14) which provides allthe necessary information for effectivecontrol of the mixer.

As already stated, only a small part ofthe EPROM capacity is used, which leavesthe user plenty of room to store new ef-fects combinations. The possibilities andrules that apply to customizing the effectsset are detailed further on in this article.The banks with custom -designed effectsare accessed with the aid of the block se-lect circuit.

Signals vsw and i tsw are taken from themodulation board to ensure that allswitching of video signals arranged by theEPROM runs synchronously with the ver-tical as well as the horizontal sync pulses.

Practical circuitThe circuit diagram of the keyboard cir-cuit is given in Fig. 12. Although a si-zeable circuit, it is the simplest in thevideo mixer.

Push -buttons S5 -Ss, like S4 -S12, form agroup of four switches of which only oneis selected at a time. This selection is ar-ranged by a combination of a NAND gateand a 3 -input OR gate. Each switch has anassociated activity LED which is driven byan output of buffer IC; The 8 switchingsignals supplied by S5-Si2 leave the PCBvia connector KSIVI.

Switches Si -S4 provide the two addresssignals AO and Al which select EPROM -resident effects and patterns. SwitchesS.:4:, -S35 are alternately connected toground or the positive supply rail. Actua-tion of one of these switches is recordedby the bistable that follows it. The bi-stables are configured as set -reset (SIR)types whose output signals are fed directto other parts of the circuit as well as tobuffer IG4 which drives five switch -statusLEDs.

The two ICs in the top left-hand cornerof the circuit,IGA and ICO2, form a priorityencoder for switches S14-824. If one of theeight encoder inputs is made high, theoutput supplies the binary value of thenumber of the relevant input. If two keysare pressed simultaneously, the highestvalue is passed to the output. Since twoindependent decoders are used, IC61 and

S14: XX00-XXOF

S15: XX10-XX1F

S16: XX20-XX2F

317: XX30-XX3F

$18: XX40-XX4F

S19: XX50-XX5F

320: XX60-XX6F

S21: XX70-XX7F

S22: XX80-XX8F

S23: XX90-XX9F

S24: XXAO-XXAF

S25: XXBO-XXBF

S26: XXCO-XXCF

S27: XXDO-XXDF

S28: XXEO-XXEF

S29: XXFO-XXFF

S1 S2 Si S4 S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4

75 75 35 35

77 7D 3D 3765 05 45 2567 07 47 27

6D OD 4D 2D

6F 6A 2A 2F

09 69 29 49

66 06 46 26

50 40 00 10

B5 BD F5 F5

BD B7 B7 BD

35 35 75 35

7F OF 4F 3F

OA 6-4 2E 4A

6F 6F 2F 2F

OE 6E 2E 4E

35 75 35 7537 7D 3D 7725 45 05 6527 47 07 67

2D 4D OD 602F 2A 6A 6F49 29 69 0926 46 06 66

10 00 40 50

F5 BD F5 135

BD 37 77 BD

35 35 35 75

3F 4F OF 7F

4A 23 6E OA

6F 2F 6F 2F

4E 2E 6E OE

75 35 75 3577 3D 7D 3765 05 45 2567 07 47 27

60 OD 4D 206F 6A 2A 2F09 69 29 4966 06 46 26

50 00 40 10

B5 FD B5 F5

3D B7 B7 7D

35 75 35 35

3F OF 4F 7F

OA 63 2E 4A

6F 62 2E 2F

OF 6F 2F 4F

35 35 75 7537 3D 7D 7725 45 05 6527 47 07 67

2D 4D OD 6D2F 2A 6A 6F49 29 69 0926 46 06 66

10 40 00 50F5 FD 35 B53D 37 77 7D75 35 35 35

3F 4F OF 7F4A 2E 6E OA2F 22 62 6F4F 2F 6F OF

Table 1. Content of the EPROM type 2764 in the keyboard circuit. Analyze the function of

each databyte to learn how to program your own set of picture mixing and wipe effects. Use

the data in Table 2 (below) for reference.

Mixed inputsbits: D7 -D6

Referencebits: D5 -D4

V -waveformbits: D3 -D2

H -waveformbits: D1 -DO

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0.5

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Lownibble

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00 00 0 x X 0 x x

00 01 1 x 0:I X 1 x x

00 10 2 x X x 2 x x

00 11 3 x ( X ) x 3

01 00 4 x I x x 4

01 01 5 x (x) x 5

01 10 6 x x x 6 x

01 11 7 x (x) x 7 x

10 00 8 x x x 8 X

110 01 x (x) x 9 X

10 10 A x i x x A X

10 11 B x ix) x B

11 00 C xixt x C

11 01 D x ixi x D X

11 10 E x x' x E

11 11 F x ixi x F

x = function selected.

(x) = function selected but overridden.

Table 2. Correlation between EPROM content and picture mixing effects.


VIDEO MIXER PART 3: KEYBOARD

Construction

S14 0000: 75 75 35 35 35 75 35 75 75 35 75 35 35 35 75 75

.t 1 1 1 1 1 1 1 1 1 1 1 1 1SI S2 54 S3 SI S2 S4 33 SI S2 SA S3 51 52 S4 53

HSW = 0 HSW = 1 HSW = 0 HSW = I

vSW - 0 vSW = I

87304.11143

Table 3. Sixteen bytes are reserved for each switch in keyboard area 1. Use the data inTable 2 to establish the associated mixer functions.

IC-: are cascaded via their El/E0 (enablein/out) pins. This ensures that ICoi is dis-abled if one of the keys S21-S29 is pressed.

The outputs of the priority encoder areconnected to a 4 -bit latch, IC5s, via threeOR gates. The fourth data input of thelatch is connected to the GS (group select)output of ICo. As a result, ICs s supplies a4 -bit key identification code. Gates N9.3-N% suppress key bounce pulses and otherinterference. The 4 -bit key code is fed di-rect to address inputs A4-A7 of theEPROM. Address inputs A8-All aregiven their respective levels by DIL switchblock S. Address line Al2 is grounded,so that only the lower 4 Kbyte of the

EPROM is used. The EPROM through theReaders Services, all switches in 535 mustbe closed. Alternatively, four wire linksmay be installed.

EPROM address line A3 is connectedto the vsw signal. Bistable IC57a ensuresthat level changes of the vsw signal aresynchronized to the line -sync signal toprevent video source switching in the cur-rent picture line.

Address line A2 is switched by the iiswsignal, while the levels of AO and Al aredetermined by switches Si-S4. The rela-tion between the EPROM address and theeffect on the picture is discussed furtheron.

The last module of the video mixer deskconsist of two printed -circuit boardswhich are available ready-made as onepiece through the Readers Services. ThePCB is double -sided and through -plated.First, use a jig -saw to cut out the partwhich is to hold the mains transformerand the two PCB terminal blocks. Theedges of this part of the board are indi-cated by holes.

Mount the transformer and the termi-nal blocks on the supply board and put itaside for fitting into the enclosure later.

The hole in the keyboard PCB createdby removing the supply board forms aclearance for the slide potentiometers.

Mount the following parts at the EPSside of the board: IDC cable headers

KSW2 and levICI, and voltage regu-lator IC-.

Be sure to observe the opposite orien-tation of SW resistor arrays R162 and R163.

Switches S13, 536 and 537 are self-lock-ing types.

In some cases, the size of C12 forces thiscapacitor to be mounted at the EPS side ofthe board.

Since the LEDs are integral to the swit-ches, these parts are mounted at the sametime.

To reduce cost, all ICs, except theEPROM, may be mounted without soc-kets.

Fig. 13. Front -panel lay -out shown at approximately 30°. of true size.



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Fig. 14. Component mounting plan for the double -sided, through -plated keyboard PCB. Note that the transformer section is cut out.

ELEKTOR ELECTRONICS \I ARCH 19911

VIDEO MIXER PART 3: KEYBOARD 29

COMPONENTS LIST

Resistors:11124-R12a;11147-R152 = 3300Fli29--Fli44:R153;R1s5:R157;Rlea:R1e4;Ries = 10kR145;R146 = 100k8154;Flise;Rioa = lkORiss:Flieo = 27051R161;11162= 4k7 (8 -way SIL resistor array)

Capacitors:C122-C137 = 100nC120 =10nC121 = 330n

Semiconductors:1C45;1Cse= 4093ICes:ICs4= 74HC2391C47;1C57;less = 74HC74ICas = 74HCT244ICes:ICsi;lCss = 4075

IC: -70052 = 74HC00IC55;1Ces = 74HCT365IC55 = 2764 (order number 5861; seeReaders Services page)ICss = 74HC175ICss = 4071IC61;1052 = 4532ICe3 = 74HCT154IC56 = 7805D7-D3s;D52-D55= LED (in switches S1 --S37)D4o-D51 = 1N4148

Miscellaneous:S1-S12;S14-S35= push-button with integralred LED (Dataswitch 61-10404010').S13:S36;S37 = toggle switch with integral redLED (Dataswitch 61-20404010').Saa = 4 -way DIP switch block.Tri = mains transformer 2x9 Vi2Y9 VA)Kt ;K2 = 3 -way PCB terminal block.

KMCI ;KSW2 = 20 -way PCB header.KSWi = 26 -way PCB header.Qty. 2:Qty. 4:Qty. 1:Qty. 1:Qty. 1:

26 -way IDC plug.20 -way IDC socket.25 cm 20 -way flatcable40 cm 20 -way flatcable60 cm 26 -way flatcable

Enclosure: e.g., ESM EP30;20-PCB Type 87304-3 (see Readers Servicespage).Front -panel foil Type 87304-F (see ReadersServices page).

' iTIN Switches Division of ITW Limited Norway Road Hilsea PORTSMOUTHP03 51 -IT. Telephone: (0705) 694971.

ESM 119 Rue des Fauvelles 92400Courbevoie France. Telephone -33 147.68.50.98. Telex: 630612.

The remainder of the construction isstraightforward. Work accurately and uselittle solder to prevent short-circuits. Al-ways remember that fault-finding in a cir-cuit like this can be costly andtime-consuming.

Custom effects: over to youTable 1 shows the structure of the con-tents of the EPROM Type 2764 for thisproject. The 8 databits of the EPROM con-trol a number of functions of the mixingdesk. The relations between the bits andthe functions are summarized in Table 2.The two least -significant bits, DO and Dl,select one of four horizontal effects volt-ages. Similarly, D2 and D3 select one offour vertical effects voltages. Databits D4and D5 select the source that determinesthe horizontal reference voltage for theswitching of 115W: this source is either thevertical effects voltage or the horizontalwipe potentiometer. Databit D5 controlsthe inversion of the picture. The two most -significant databits, D7 and D8, select theinput signal source. The table and the bitassignment should enable you to analysethe function of each databyte in the 'stand-ard' EPROM fairly quickly.

The logic levels present at the EPROMaddress inputs determine which of the da-tabytes is applied to the EPROM da-telines. This address emanates fromswitches Si -S; and S14-Sz9, and the HSWand vsw signals. The functions of the en-tries in Table 2 are explained below. First,however, assume that the remaining ad-dress lines are low.

The table contains 16 lines, one foreach effect switch in area 1. The remainingaddress locations in the 'standard'EPROM are empty. Each line invariablycontains 16 bytes, each of which can beselected individually by applying the rele-vant address. Table 3 lists the functions ofall variables. If, for instance, switches Siand S14 are pressed (horizontal wipe), thefirst byte in the EPROM is initially put onthe databus. Write down the binary struc-

4#

-4-". a..

.

. 4

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ture of the byte. From Table 2, it is ana-lyzed as follows:

Input II/III is used;the horizonal reference voltage is sup-plied by the potentiometer;the horizontal effects voltage is a ramp;the vertical effects voltage is a ramp.

When HSW is active -as a result of thehorizontal ramp exceeding the referencelevel set with the potentiometer -the fifthbyte is applied to the databus. Again refer-ring to Table 2, input 1 /2 is selected. Thismode causes a horizontal wipe effect withthe position of the picture transition beingdetermined by the slide potentiometer forthe horizontal effects.

The function of the EPROM -based con-trol words is similar for the vertical effects(assume that S2 and 54 are pressed). Desig-ning and storing one's own picture effectsis not simple. The tables and analysis ofthe 'default' effects in the EPROM, how-ever, should provide sufficient informa-tion to get you started.

The last instalment of this article will appear in nextmonth's issue of Efektor Electronics. Parts 1 and 2appeared in the January and February 1989 issuerespectively.

Fig. 15. Example of a picture -mixing ef-fect in four stages.

EI.EKTOR ELECTRONICS MARCH 1990

30

DESIGN IDEASThe contents of this column are based solely on information supplied by the author

and do not imply practical experience by Elektor Electronics

LOW-COST V/I DISPLAY MODULE

by NIohd Abdul Sami

The circuit described here is a modification to the "Digital V/IDisplay" published in this magazine some years ago(1). It can

display more than one analogue input (on different read-outs),although it uses only one analogue -to -digital converter.

The circuit diagram shows that the multi-plexer. IC4. is clocked by the MSD (mostsignificant digit) output of analogue -to -digital converter (ADC) ICI via switchIC5c. As soon as the MSD output revealsthat the relevant input has been convertedand channelled to the output. the counterincrements and another analogue input isselected by the ADC. The design is suchthat only one switch and one BCD -to -7 -

segment decoder (1C2 or IC3) are enabled

at any one time.When the counter increments, its out-

put disables the blanking input of the ap-propriate 7 -segment decoder. At the nextincrement. Q3 resets the counter and thecycle repeats itself.

Although it is possible to have threeread-outs, the clock of the CA3162 is notreally fast enough to ensure correct persis-tence of all three displays, although theyremain perfectly readable.

If a third read-out is used. Q3 of IC4must be connected to the control input ofan additional sw itch. Q4 to the blankinginput of the decoder, and Q5 to the reset ofthe counter.

The input voltage ranee is 0-0.999 V.The reference potential of all inputs is theLO input of ICI.

I ) July/August 1987. Supplement. p.5

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3xA564

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E Ji\\ Awith a contribution by B. Lewetz

o-

The plotter we published roughly two years ago is among our mostpopular projects thanks to a relatively simple mechanical

construction and the availability of an associated stepper motordriver board. Although a number of readers have sent us

suggestions for software drivers that would enable the plotter to beused with popular computers, only Mr. Lewetz' contribution provedto meet the requirements as regards use of the driver on IBM PCs,and (at least partial) compatibility with the industry -standard HPGL

plotter command language. Before introducing the software,however, we avail ourselves of the opportunity to propose some

improvements to the mechanical design of the plotter.

Like its predecessor (Ref. 1), the Mark -IIversion of the plotter uses paper move-ment for the Y -direction, and pen move-ment for the X -direction. As such, theoperation of the plotter is not unlike thatof a matrix printer. The platen whichcauses the paper movement is operateddirect by a stepper motor. The pen car-riage is coupled to another stepper motorvia a string. Small solenoids control thepen up/down movement. The simplemechanical construction and the possi-bility of customizing the plotter width inaccordance with the maximum requiredpaper width are important factors thatmade us prefer the above arrangementover the more complex X -Y variant.

The plotter works in conjunction witha control board which translates a bit -pat-tern applied to its input into the corre-sponding control signals for the threesolenoids and two stepper motors. Thecircuit is based on two special steppermotor driver 1Cs from Motorola whichobviate complex bit -shift and timing oper-ations for the control of the half-step and

full -step modes as well as the for-ward /reverse movement of the steppermotors at the required accuracy. Thechips, Type MC3479, allow the 8 -bit wideinput of the control board to be driven bya Centronics (printer-) port, which isavailable on almost any IBM PC -XT, AT orcompatible. Connection details are givenin Fig. 2.

The control board used for the newversion of the plotter is that discussed inRef. 1: no changes are required, and thecircuit works in conjunction with the soft-ware package described further on.

Mechanical workSince the mechanical construction of theplotter is discussed at length in Ref. 1,there is no need to repeat it here. The newworking drawings, Figs. 1 and 3, and theassociated parts list reflect most of themechanical changes made to the originaldesign. The most important change is thatthe Mark -II version is about 10 cm wider,which allows AZ paper to be used side-

ways and A3 paper lengthwise. Fourpaper rollers are used instead of two forimproved accuracy of the Y -movement.Also, the platen is fitted with a 12 mmdiameter bearing at the free side to reducefriction (see Fig. 4: the original had anylon bushing).

Further improvements to the originaldesign have been suggested by numerousreaders. The use of a lathe to reduce thediameter of the platen at the locations ofthe sandpaper grips, for instance, may begone round by covering the platen in flex-ible conduit. The same is suggested for thepaper rolls. It should be noted, however,that these modifications may result in dif-ferent step sizes for the horizontal andvertical movement, which may requiresoftware -controlled compensation.

Further suggestions as regards im-proving the mechanical stability of theplotter entail the use of 4 -mm thick alumi-nium, stainless steel or silver steel. One ofour readers in Greece, a lathe operator byprofession, has built the plotter fromstainless steel, using sintered metal for the


iCOMPUTERS AND MICROPROCESSORS

MAIN SPECIFICATIONS,

Hardware:beam plotter for paper size up to DIN -A2(594x420 mm)

repeatability: <0.1 mm

3 colours

simple construction

control board with centronics input

Software:partially HPGL compatible 16 commandssupposed)

plot commands sent via Centronics port

compatible with Eiektor Electron4.7s plot-ter driver board

software soapier

configuration file

programmable plot speed

multitasking Turbo -C control program

auxiliary programs for:- keyboard control- plot file formatting- fulftalf-step operation

bearings, and PTFE (teflon) for the rollers.The use of high-grade metals, however,requires a wide range of tools and otherspecial materials from your local hard-ware shop, and, of course, access to a

lathe.The nylon string is a crucial part and

requires special attention because it mustbe secured in a manner that eliminatesany risk of slipping on the spindle of theX -motor. One string end is secured to thecarriage at the side of the string wheel.From there, the string goes to the stringwheel where it makes a left turn towardsthe X -motor. The carriage is pushed to theextreme left (X -motor side), and the stringis wound on to the motor spindle (part id.10) until one particular point in the stringis always in contact with the spindle. Thismeans that the total length of the woundpart of the string is equal to or greater thanthe maximum X -distance that can betravelled by the carriage. The point in thestring is secured at the top of the motorspindle with the aid of an M3 screw.

SoftwareThe software driver developed for theplotter runs on IBM PCs and compatibles.The driver is written in Turbo -C (Borlandversion), and is capable of reading plotfiles with a reduced command set to theHPGL, Calcomp or Gould standard. Theprogram converts the data and commandsin these files into coordinate numbers inthe relevant plot area before it sends, viathe Centronics port, the necessary motorand pen control commands to the plotterdriver board.

To be able to generate a usable plot file,the CAD program which is used to makethe drawing must have plotter types

''''V 'To.-..,..-..i .z.0 c:, ,:-.: :... C

11

\i 2 Z

Fig. la. General parts identification of the plotter.

Fig. 1b. Parts identification for the side plates which hold the stepper motors.

AS = 3PW = 0WB = 1002X = 02Y=03X = 03'e

MX = 1700

MY = 2000SD = 4

SS = 1

GS = 0PT = 55LA = 1

BV = 1

PS = 1

RA = 1

SX = 100SY = 100

Number of oens

Pause at pen change (0/1)Wait time after pen actuation (clock cycles; 1-255)X -difference between pen 1 and pen 2 (-500-500)se -difference between pen 1 and pen 2 (-500-500)X -difference between pen 2 and pen 3 (-500-500)Y difference between pen 2 and pen 3 (-500-500)Maximum X-coordinate (0-1000)Maximum Y-coordinate (0-10000)Step duration (clock cycles; 1-255)Parallel port number (1.'2)Foil -step mode

System clock t1-255)Loudspeaker on!off (0;1)Slow:fast (0.1)

Piot language (1=Calcomp: 2=Gould; 3=HPGL)Draw frame (0/112)

X -scale (1-1000)se -scale (1-1000%)

Table 1. Parameters in the driver configuration file. MONDRIAUSYS.

E EKTOR ELECTRONICS MARCH 1990

PLOTTER MARK -II

HP7220, Calcomp 81 or Gould 6200 in itsdevice driver list. On completion of thedrawing, the plot file is not sent direct tothe Centronics port, but to a file which istemporarily stored on disk.

The plotter driver program, MON-DRIAN.EXE, is called up with the plot filename as an extension, for instance:

MONDRIAN NOZZLE.CAL

To enable the driver program to find theplot file, it must either be listed in thesame subdirectory, or the PATH configura-tion must be set accordingly.

The program starts with a menu screenwhich shows the current options and par-ameters. The lower window on the screenshows the plotter commands as they areread and converted.

The program works on two tasks in aquasi -simultaneous manner: the conver-sion of plot coordinates into step pulsesfor the motors, and, in the background,the sending of calculated values to theplotter control board via the Centronicsinterface. A problem may arise from theassignment of processor time to thesetasks. If the calculations run too fast, theplotter forms a bottleneck after a relative-ly short time. Conversely, if the calcula-tions run much slower than the actualplotter control, the plotter wastes timewaiting for new commands from the com-puter. The time sharing problem is elimi-nated by an auxiliary program,REALTIME.0O3.1, which establishes an opti-mum time ratio for the two processes onthe basis of the computer type used.

PC connector

14

Centronics

0

plotter

DO

K1

0 00 0

01O02

O o0 0

D3 004

,00 0-16 0- 05 op

D6 0A18...25_ 0

0 07 000 0ORM 0

0000 Busy -input 0 0

0 00-25 0 00

E'14:175 13

Fig. 2. Connections between the PC Centronics port and the input of the plotterdriver board.

The driver program may be called upwith a test switch:

MONDRIAN /T

to check quickly and without wastingpaper whether the drawing fits on the re-quired paper size. If not, the scale factorsmust be modified accordingly.

Parameters andconfiguration fileThe plotter driver program is simple toconfigure for different mechanical con-structions (as already noted, the construc-tor determines his own plotter width). The

configuration file on the disk, MON-DRIAN.5Y5, contains the start parameters-an example is shown in Table 1. The filecontains ASCII characters only and maybe edited with a word processor. Each linestarts with a two -letter parameter identi-fication and a default value, which cantake up to three digits. As shoum in theexample, each line is made complete withcomment.

When called up, the control programsearches for MONDRIAN.SYS and loads theuser -defined configuration. If the file cannot be found, default values are adoptedfor the parameters otherwise loaded fromMONDRIAN.SYS. A fair number of configu-ration options is available, from the num-ber of pens to the zoom factor and the plotlanguage. The nX parameters (X -Y dif-ference) allow drilling inaccuracies in thepen holes to be compensated: in this man-ner, the inaccuracy caused by a pen (=colour) change can be kept smaller than0.1 mm.

LimitationsIt should be noted that version 1.0 of MON-DRIAN.EXE recognizes only six HPGL(Hewlett-Packard Graphics Language)commands, while the language has manymore. The same goes for the Calcomp andGould formats: only six commands aresupported. Fortunately, many problemscaused by this limitation may beprevented by using the right plotterdriver. Most CAD programs allow theuser to select a particular plotter driverfrom a menu during installation of the

SOFTWARE ON DISKETTE

The plotter driver program and con-fiauration utilities described in thisarticle are available on a 514 -inch360 KByte MSDOS formatted floppydisk under order number ESS117.Details on cost and ordering aregiven on the Readers Services pageelsewhere in this issue.

c!riva A is ESEL:''

;-:-;5 -1E -E;

e st

LLEKTOR ELECTRONICS MARCH 1990

34 COMPUTERS AND MICROPROCESSORS

1,260

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416

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countersunk screws

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ALL DIMENSIONS IN MM

tt

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11.12

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0

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14

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Fig. 3. Dimensions of all nylon and aluminium or stainless steel parts that must be cut. filed, turned and drilled.


IIPLOTTER MARK -11

MECHANICAL PARTS LIST

(all dimensions in mm)

1. side plate; left; aluminium: 60x70x3 mm.2. side plate; right; aluminium: 60x70x3 mm.3. angled support bracket for X motor, L-shaped aluminium: 20x40x4 mm; length60 mm.4. square connection bar: aluminium10x10 mm; 508 mm5. round connection bar; aluminium stain-less steel rod; dia. 6 mm; 508 mm long.6. round support bar for pen carriage; dimen-sions as 5.7. round guide bar for pen carriage; dimerrsions as 5.8. round bar for pressure rolls; alumi-niumistainiess steel rod; dia. 6 mm: length501 mm.9. platen; round aluminium bar; dia. 12 mm:length 514 mm.10. shaft aluminium: dia. 12 mm; length40 mm.11. tilt lever for pressure rolls spindle; U-shaped aluminium beam 10>:10x1 mm;length 48 mm.12. see 11).13. angled support bracket for string wheel;

U-shaped aluminium beam 15x15x2 mm:length 14 mm.14. pen carriage: U-shaped aluminiumbeam 25x50x3 mm; length 60 mm.15. pen positioning plate; aluminium;8x50/2 mm.16. cable guide: U-shaped aluminium beam12x8 mm; length 508 mm.

Miscellaneous parts:6 off slide bearings; nylon; Skiffy 08-6.1 off bushing for platen; nylon; Skiff; 08-4 or08-6, or suitable ball bearing.2 off washer rings for V -motor; internal dia.3 mm; thickness 2 mm.2 off rubber pressure rolls (e.g. cable grom-met).4 off fixing rings for dia. 6 mm spindle (e.g.Skiff)? 11-1-6).1 off string wheel.3 off cylinder head screws M4g5.2 off cylinder head screws M4x10 (for fixingpart no. 3).1 off cylinder head screw M4x20 with 3 nuts.5 off M4iS screws with countersunk head.4 off cylinder head screws M3>:40 (for fixingstepper motors).

2 off cylinder head screws M3x50 (for fixingpart no. 15).2 off cylinder head screws M3x10 (for fixingstring).2 off cylinder head screws 1t.,13x15 (for fixingspring brackets).4 off headless adjustment screws M3x3 (forfixing pan nos. 9 and 10).6 off bolts M2.6x5 (for fixing pen lift mag-nets).16 off hexagonal nuts M3.2 off springs for pressure rolls spindle.string: e.g., wound fishing linefine grade sandpaper (for securing onplaten).

Electromechanical parts:2 off stepper motors; 200 stepsirev.: dual -phase bipolar; 200 mA!phase (e.g. Bergeras used in disk drives).3 off pen lift electromagnets: 12 V; e.g. Bin-der Magnate Type 40031-09600.

Distributor of Skiffy products in the UK isSalterfix Fasteners Salter Springs & Press-ings Limited Spring Road Smeth.vick Watley West Midlands 866 1PF. Tele-phone: (021 553) 2929. Telex: 337877.

Fig. 4. A ball -bearing may be used wherethe plate is secured to the side plate.

Fig. 5. Detailed construction of a paperroll.

package. Programs like AutoCad andAutoSketch, for instance, use only six plotcommands if a Hewlett Packard plotter isinstalled: circles and ellipsoids are drawnwith the aid of MOVE and PLOT sequencesrather than with the much more powerful

ARC command. This means that only asubset of basic HPGL commands is used.Since the present driver program, MON-DRIAN.EXE, is capable of handling the sixbasic commands, it should be suitable formany CAD packages, provided they canbe configured to save plot files with thereduced set of HPGL commands.

Reference:

1. Plotter. Elektor Electronics May 1988 andJune 1988.

Elektor P1.:.... :r:Yer Ve:e'.c:-. : ' :;:pyr'_ght by Elektor. 1939

- :.... :.e.,; ;ens f:e name 7.::::a.:e:

:....-E:e- CFF - ^- con_:_..,:_... :A:::',! --

frame CiN ........ C.....99 :s

nuaber of pes-os 3 clocks per step 4

parallel i:-.erface clocks per pen movement:00

4: : :4- .. love to :1347/1115

41 : H pen up

43 : 133 ::2-:F. move to :1315f1113

44 : : pen down

4` : 1-4 :24E -Ave to :1:if4 :1-4

4. : :".'.:E :ii.1K nave to :::.:. :ii

4- : ::- :2:,:E -.:Ye to :::::- :13:

49 : 1:-4 :::::Y -_-..ve :: :1-4 :7::E_

5. : 155; :1-.4Y. 7.:7i 7: ::'E5; :94

51 : H pen up

continue - press any key... : - cancel p - pause s - stop

Fig. 6. Screen dump of the plotter driver program, MONDRIAN.EXE.


36

GrAOS

The circuit described here enables an os-cilloscope to be triggered when a pre-determined binary code word is appliedto one of the circuit's inputs.

Integrated circuits ICI and ICz comparethe 16 input levels with the code set byswitches Si and S2. If one of the inputs hasa dataword that is equal for not less than100 ns to that set by Si and SS, pin 19 of ICIgoes high. Note that, because of the pull-up resistors, open inputs are treated ashigh.

When pin 9 of ICI is high, monostableMM1/2 is triggered and outputs a negativepulse from its pin 4. The length of thispulse is 0.1-1.5 l.ts, depending on the set-ting of Pi. If during that time the pre-determined trigger value disappears, notriggering takes place. Potentiometer Pi isa logarithmic type to enable very shorttimes to be set accurately.

The output pulse from MMVs triggersa second monostable, MMVi, whosemonotime has been set to 1 .ts by R23 -C3.

Either the positive signal from the Qoutput or the negative signal from the Qoutput, depending on the setting of S3,may be applied to the oscilloscope.

The printed circuit board is relativelysmall. Most resistors are mounted up-right. If difficult to obtain locally, the foursingle -in -line (SIL) resistor arrays mayeach be replaced by eight vertically fittedresistors whose top wires are cut short forconnecting to a horizontally running wireto the +5 V line.

,r'IR)

[ LOSCOPA. Rigby

5V

1001,3

*see test

FIt9Bs IMF

C2 *

MMV1,MMV2=1C3=74HCT123

BA

MMV2BCE4T

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COMPONENTS LIST

Resistors:= 10k

R17-RaP., = 100kR21,R23 = 2k2R22 = 470 faPt = 100k logarithmic potentiometer

Capacitors:C1= 10pC2 = 47pCs = 1n0C4 = 100n

Semiconductors:ICt ;IC2 = 74NCT688IC3 = 74HCT123

Miscellaneous:SI;S2 = 8 -way DIP switch.S3 = miniature SPDT switch.Kt = BNC socket.Qty. 18: miniature test clip.Enclosure: e.g., OKW A9010 065PCB 894042


?En) V-JFN 1 MONR.G. Krijgsman PE1CHY, J.C. Stekelenburg PE1FYZ and J. Buiting PE1CSI

A wave of publicity recently swept over the UK announcing the launch of thefive -channel BSB TV -satellite. Everybody seems to have an opinion on this event,

and pages of comment have been written on it, even in technical magazines, withoutproof of the availability of receive equipment. The bottlenecks are, as we learn from

informed sources, the aerial and the D -MAC set -top decoder. Well, squarial or nosquarial, Elektor Electronics is proud to be the first international electronics

publication to present pictures of MAC transmissions received from BSB and otherDB satellites. Rather than gazing into a crystal ball, we show you a glimpse of a

multi -standard MAC decoder for home construction that is currently being designed.

At the time of writing (mid -January I990h.the launch of BSB's five high -power TVchannels is due this spring. From a technicalpoint of view. BSB offers two novelties: D -MAC and the flat dish or squarial. Othertechnical aspects such as the use of the DBSfrequency band (11.7-12.5 GHz), circularpolarization and medium -level transmitpowers (approx. 55 dB\V) will certainly benew for many satellite -TV enthusiasts, butare familiar from other broadcast serviceswhich have been in use for over a year al-ready. DFS Kopernikus (23.5' E) has aboutthe same transmit power as BSB. while bothTDF-1 and TV-SAT2 use D2 -MAC. hightransmit powers (61 dBW) and circular po-larization in the DBS band. Keen satellite -TV experimenters may also have noted thevery strong signals from the two DBS TVtransponders on board the Olympus satellite.One channel is currently allocated to RAIItaly. the other to British Telecom. The RAIchannel is transmitted in PAL, while BritishTelecom alternately use PAL and D2 -MAC.the latter for parts of the BBC -TV Europe

programme. TDF-1. TV-SAT2 and Olympusare positioned at 19° west. BSB is positionedat 31 West. which is more favourable for theUK because it allows the satellite's spot -beam to cover the target area at roughlyequal signal strength, and because the dishelevation is not too low.

Strong but unintelligibleWhatever the standard, C-. D- or D2-\IAC.MAC pictures are totally unintelligible onstandard PAL monitors and TV sets used byhundreds of thousands of satellite -TV vie-wers in Europe. This is because the MACstandard uses a totally different method ofpicture and sound transmission, which ispartly digital and time -multiplexed ratherthan frequency -multiplexed. Although set -top decoders for MAC channels are not yetavailable. it is surprising to note how manynon -technical dish owners are aware of theexistence of the MAC system, and even themeaning of the acronym. This awarenessmust be partly due to two D2 -MAC channels

on the Astra TV satellite: Scansat TV -1000and TV3 (one of which is encrypted at lowlevel).

Both TV-SAT2 and TDF-1 are runningexperimental transmissions. TDF-1 has fourtransponders which are used for promotionalpurposes and technical experiments. TV -S AT2. the \Vest -German DB satellite. car-ries four T\' channels which run in parallelwith DFS Kopernikus and Astra. Remark-ably. some of the programme material onTV-SAT2 is in PAL, while the satellite trans-mits in D2 -MAC. So much for technical im-provements!

The transmissions received from BSBduring its pre -operational use that started inDecember 1989 are also experimental. Threetransponders are already encoded, and one isin 'clear' D -MAC. As could be expected. thesignals are strong and totally noise -free.

Experimental equipmentThe equipment used for making the accom-panying colour photographs was assembled

DBS

LNB

60-c m

4 ,

) oish

INDOOR UNIT

modifiedbasebandoutput

-De-emphasis-AGC

"CLIMB"

O

AGC

C/D/D2-MACDECODER

4 -wire

IMB

RGB

monitor

900049 11

Fig. 1. Layout of experimental equipment used for making the colour photographs in this article.

ELIA:TOR ELECTRONICS MARCH 1990

38

Photograph 1. BSB still test picture (D -MAC).

Photograph 3. ARD-1 Fu-Bk-type test chart (TV-SAT2: D2 -MAC).

EunOSTEPTuesday January 16 1990C.E.T09.00 NOTTINGHAM PAST AND

PRESENT09.30 AROUND OUR SCHOOL10.00 PLATO PROGRAMME11.30 SOBA12.30 EUROPEAN PROPERTY

DEVELOPMENT ANDPLANNING

13.00 VETERINARY TEACHINGMATERIAL FROM CAMBRIDGE

14.00 CLOSEDOWN

Photograph 5. European info programme (D2.MAC: Olympus).

Photograph 2. BSB colour -bar test chart (D -MAC).

Photograph 4. TDF-1 station identification (D2-11.1AC).

Photograph 6. RAI Fu-Bk-type test chart (PAL: Olympus).


39


Photograph 9. Outdoor unit set up on a photographer's tripodin the garden.

nen-co '..-3e1--iTccw.:413-Jau-rtilii!Kt)ikal, Vt1

C113n(V)oi) II() (quo CL48

fRitaiyr Ji-rqu I 1111,,IY:III(Ici(3 It_1113

RoBuiliti-EM0021) 8 Vi

NORDIC CHANNEL.

Photograph 8. Nordic -channel identification (ECS4: D2 -MAC) .


Photograph 11. Video clip in brilliant colours on TDF-1 (D2 -MAC).


40

Satellite Position Country EIRP Channels TV standard Programmes.

TV-SAT2 19`W West -Germany 61 dBW 4 (Ihc) D2 -MAC Sins -Plus, 3 -SAT, RTL-Plus, SAT -1BSB-1 31' W United Kingdom 55 dBW 5 (rhc) D -MAC The Movie Channel. The Sports Channel, Galaxy,

Nov, The Power StationTOF-1 19= W France 61 dBW 4 (rhc) D2 -MAC Miscellaneous; to be assignedOlympus 19 W UK:Italy 63 dBW 3 (lhcrhc) D2 -MAC; PAL RAI. B.T. World Service:BBC TV Europe,Discovery

experimental services.rhc = right-hand circular polarization. the = left-hand circular polarization.

experimentally to test a prototype of a multi -standard MAC decoder which is currentybeing developed in the Elekior Electronicsengineering department. A preliminary de-scription of this unit. which we hope to pub-lish later this year, is given further on.

The general layout of the equipment isshown in Fig. 1. The outdoor unit used forthe experiments consists of a 60 -cm off -setdish and a Type ST -980 LNB from Uniden.The latter is a fairly unique unit because itcan be switched from CSS-band (10.95-11.75 GHz) to DBS-band (11.75-12.5 GHz)reception by means of two supply levels onthe LNB downlead coax cable. The noisefigure of this LNB is also remarkable at1.9 dB. A linear polarizer could be used withimpunity because there is (as yet) no inter-ference from other satellites at the UK DBSposition of 310 NV (for the Euro-DBS posi-tion, 19° W. we use a piece of teflon in theround feed -horn to turn the linear polarizerwith magnetic H/V selection into a circularfeed). It must be noted, though, that the useof a linear polarizer for circular signals re-sults in a signal degradation of at least 3 dB.

The indoor unit is a Type CX-8520R fromConnexions. The baseband output of this re-ceiver is modified to provide the large band-width required by the MAC decoder(insufficient bandwidth results in high bit -error correction rates).

Next in the configuration is a purpose -de-signed de-emphasis/AGC unit which is con-trolled by a digital signal supplied by theMAC decoder. This unit, which exists as anexperimental design. is a quite elaborate cir-cuit to meet the EBU specifications in re-spect of the de -emphasis for D -MAC as wellas D2 -MAC (these specifications are not thesame as those used for PAL). The AGC func-tion makes the operation of the de -emphasissection independent of the baseband signallevel. This is an important aspect which en-sures that many types of indoor unit can beused with the decoder.

What's cooking?The heart of the system is formed by anexperimental multi -standard MAC decoderbased on the Type DMA2280 chip from ITT(Intermetall). The decoder, of which an in-side view is shown in Fig. 2. is controlledover a 4 -wire cable by a PC running theCLIMB (Command Language for InterMe-tall Bus) interpreter from Intermetall. Thisinterpreter allows sequences of read/writeoperations to the nearly 100 registers in thechips on the decoder board to be given aprogram structure, and works in conjunction

with a PC insertion card. The PC is, ofcourse, required during the design stagesonly to establish the optimum program flowand register contents. If these parameters areknown, almost any small microprocessorsystem can take over this task, running anEPROM -based program. The authors/de-signers are currently thinking of using a Z80and some peripheral chips for this applica-tion.

The MAC decoder supplies RGB sienalswhich are fed direct to a high -resolutionmonitor via its SCART input. Note that thedecoder has registers for just about everypicture setting. from colour saturation andbrightness to horizontal sync delay and pic-ture positioning. Remarkably. the decoderobviates anything to do with PAL. SECAM.or remodulators because it drives the RGBcircuits in the TV direct to ensure the bestpossible picture resolution. The MACdecoder has an option for automatic 16:9 -to -3:4 aspect ratio conversion, which allowsfuture HDTV transmissions to be seen on astandard (3:4) TV set or monitor. Some ex-perimental 16:9 transmissions have alreadybeen received from TDF-1.

Fig.

ImpressionsTalking about picture resolution, the qualityof a real MAC picture (not a PAL programmetransmitted in MAC) is impressive even ifyou are used to day-to-day TV reception atgood quality. The colours in the still picturesand the test charts transmitted by the BSBare, in a word. brilliant, and do not sufferfrom boundary effects and other colour ir-reeularities. Cross -colour and moire effectsare completely absent, and the picture resol-ution is suddenly 6.5 MHz as compared to a`lousy' 3.5 MHz that can be resolved bymost current PAL TV sets. Transitions be-

een deep red and blue, notorious in thePAL system for their blurred picture areas.are sharp as never before (note the colouredoval in the BSB logo, and R -to -B transitionin the the TDF-1 ident). The sound accompa-nying the MAC programmes is in stereo atCD quality. Each BSB channel may have upto eight of these high -quality sound chan-nels.

Colour photographs for this article made byRobert Krijgsman on 4 January 1990.

2. Inside view of the prototype multi -MAC decoder.


POWER LINE MONITOR41

J. Ruffell

Most of us are aware that computers and other digital systems cango haywire just like that. If neither the hardware nor the software canbe blamed for the hang-up, spikes on the mains voltage are the most

likely cause of the trouble. The power line monitor described hereenables you to determine whether or not spikes occur frequently ona particular mains outlet, and whether or not digital equipment needs

to be powered via a mains filter to reduce the risk of hang-ups ortotal break -downs.

Sudden transient disturbances of themains voltage are commonly referred toas surges or spikes. Since their peak volt-age can exceed the normal mains voltageby hundreds of volts, it is not surprisingthat mains -powered equipment behaveserratically or breaks down altogether. Un-fortunately, the occurrence of spikes isfairly difficult to record reliably, the rea-sons for which are mainly:

the occurrence of a spike is difficult topredict;the voltage rise has a very short duration(typ. 10-500 ns);voltage peaks in excess of 1,000 V are noexception;the recording instrument must be con-nected to the mains line.

Principle of operationThe principle behind the power line moni-tor is shown in Fig. 1. Resistor R9 forms aload for the rectified mains voltage. As-suming that the mains frequency is 50 Hz,the frequency of the voltage on R9 is100 Hz because a full -wave rectifier, DI -D4, is used. Spikes typically have a muchhigher frequency and are, therefore, read-ily detected with the aid of a high-passfilter, Ci-Rt, where Rt is the input resist-ance of the detector circuit. The 3 dB roll -off frequency of this high-pass is about16 kHz, while its time -constant, t, equals

Fig. 1. Principle of spike detection.

RtCi =10 is. The function of 12,4 may be lessobvious in this basic circuit. Without it,however, Ci would be charged to the peakvalue of the mains voltage (approx.340 V). This would cause the diodes in thebridge rectifier to start conducting againif the mains voltage rises above this peakvalue. As a result, a 200-V spike duringthe mains zero crossing could not be de-tected since it would end up in the bridgerectifier. R9 is, therefore, fitted to ensurethat the voltage on Ci follows the rectifiedvoltage accurately. Hence, spikes are not

MAIN SPECIFICATIONS

trigger level adjustable in six steps:50 V; 100 V: 250 V: 500 V; 1000 V

responte time: <50 ns

potential -free detector output via opto-coupler (UCE(=ax;.=32 V)

built-in mains power supply

visual and audible spike indication


(10. GENERAL INTEREST

blocked by the rectifier, and they are toofast to be 'followed' by Cr. The result isthat each and every spike or dip on themains voltage appears across Rt. Dips,however, are ignored by the detector cir-cuit.

Circuit descriptionFigure 2 shows the circuit diagram of thepower line monitor. The mains voltage isrectified by a bridge circuit composed offour diodes Type 1N4007. This diode isused because of its peak reverse voltagespecification of 1,500 V. The value of R9 isa compromise between acceptable dissi-pation and sufficient loading of Ci. Thehigh-pass filter is formed by Ci and Ri-Rs.The minimum working voltage of Ci mustbe 630 VDC since the device has on it therectified voltage of about 340 V. The resis-tor ladder network, Ri-Rs, has only thespikes across it.

The ladder network and the associatedrotary switch allow spikes at a certainlevel to be attenuated before they are ap-plied to the trigger input of the detector,ICib, via the pole of Si. A Type 74HCT221dual MMV is used because of the follow-ing specifications, of which the import-ance is undisputed in the applicationcircuit:

the inputs are protected up to 2.5 kVtypical;the input capacitance is low at 3.5 pFtypical;the minimum width of the trigger pulseis 14 ns;the trigger level is accurately defined at1.3 V, which enables a simple voltagedivider to be used.

Note, however, that the actual minimumtrigger pulse width is determined by theinput attenuator and the stray capacitanceof the input protection diodes, D4 -Die, andthe trigger input of ICib. This R -C combi-nation forms a low-pass filter that causesspikes to be detected only if they arelonger than 50 Its.

Monostable multivibrator (NINIV)is triggered when the attenuated spikevoltage exceeds the trigger threshold setwith Si. On triggering, outputs Q and Qsupply a 20 -ms pulse. The pulse at the Qoutput is fed to ICI., which lengthens it toabout 1 second. During this time, LED Diiand buzzer Bzi signal the occurrence of a

OPERATION AND CONTROLS

Range switch (Sit: set to expectedspike level. Spikes exceeding set levelare detected and indicated.

Test switch (S2): press to test triggerfunction (manual trigger)

LED (Ds): °wolf Indicator

LED Di, and buzzer Bzi: spike indica-1015

Fig. 2. Circuit diagram of the power line monitor.

*Fl50mA /T04 03

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02 01 C1 R1 R2 n

R 70-0

0504

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R1604: Oi /00e ?CIR13p.704:),

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Fig. 3. Printed circuit board overlay and track lay -out (reflected).


POSNER LINE MONITOR 43

COMPONENTS LIST

Resistors:Ftt ;R2 = 4k87 1%Ra = 130SI 1%R4 = 78R7 1%R5 = 26R1 1%Re = 8066 1%R7 = 45232 1%Rs = 13c2 1%R9 = 100k 1 WRio= 820c1

= 680k1312:1117 = 47052 = 4k7R14 = 4M7Rts = 10kR16 = 270k

Capacitors: = 1n0; 630 VCz;Cs:C 7 = 100nC3 = 470u; 25 V; radialC4 = 1110

CS = 2112; 16 V; radialCs = 100n

Semiconductors: - D4 = 1N4007

Ds = LED 5 mm greenDe;Ds;Da:Die = 1144148D7 = 1N4001Olt = LED: 5 mm; redTI = BC547BIC = 74HCT221iCz = 78L05IC3 = CNY21 or IL10 (Siemens; Etectro-Value Ltd.)

Miscellaneous:Si = 2 -pole 6 -way rotary switch for PCBmounting; plastic spindle.S2 = miniature push -to -make button.Bzi = 5-V active buzzer.FI = fuse; 50 mA; slow; with PCB -mountholder.To = 9 V,0.35 VA mains transformer.

= 2 -way mains -rated terminal block.Kz = 2 -way terminal block.ABS mains supply case: outside dimen-sions: 120x65x40 mm.PCB Type 900025 (see Readers Servicespage).

spike. The detection circuit may be testedby pressing S2; this causes 'Cis to be trig-gered manually.

The Q output of ICIb drives an opto-coupler, IC3, to create a potential -free out-put, i.e., an output that is not at mainspotential and, therefore, safe (withinlimits) for connection to other equipment.Connector K2 may be wired to the inputof, for instance, an event counter to estab-lish the number of spikes that occur dur-ing a certain period. The output may alsobe used to stop a digital clock, or for othertime -keeping purposes, to enable theorigin of the spike to be traced. Anotherapplication is the use of a storage oscillos-cope to determine when and why a par-

ticular computer broke down owing to amains surge.

Because of the limited drive capacity ofthe 74HCT221, the LED in the optocoupleris not fed with its maximum current. Thismeans that the external collector resistorfor the optocoupler must not be smallerthan 10 kQ to ensure that the phototran-sistor is just driven into saturation.

Be sure to connect the external collectorresistor and the emitter of the optocouplerto the positive supply and ground respec-tively of the recording equipment(whether digital or analogue), never to the+5 V and ground lines of the power linemonitor, since these may be at mainspotential.

The +5 V voltage for the power linemonitor is provided by a standard powersupply based on a mains transformer anda fixed -voltage regulator, IC2. Note thatthe use of this supply does not mean thatthe low -voltage part of the circuit is safeto touch.

Construction and initial testWith safety in mind, it is best to constructthe circuit on the printed -circuit boardshown in Fig. 3. This board is mountedinto a so-called power supply enclosurewhich is supplied complete with line andneutral pins for plugging into a mainsoutlet.

Capacitor Cs is not shown on the over-lay, but may be connected in parallel withR13 at the track side of the board. Therotary switch must be a type with a plasticshaft, and the push-button must be fittedrecessed, so that none of its metal partsprotrude from the enclosure.

All equipment connected to K2 must bepowered from a separate supply, batteryor adapter.

The operation of the monitor is simpleto verify by plugging it into a mains socketand switching a nearby fluorescent tubeon and off a few times. Set to the mostsensitive range (50 V), the monitor is near-ly always triggered if the mains outlet ison the same line as, and within 10 m from,the tube lighting. The number of 'hits' willbe found to decrease as the sensitivity ofthe monitor is lowered, and the distanceto the tube is increased.

DC -AC converterJuly/ August 1989, p. 49-51

Only when used in conjunction with theexternal timebase circuit, the 4047 in theconverter supplies an output signal witha duty factor other than 0.5. This causesthe primary transformer winding tobecome saturated, and the dissipation inthe power transistors to rise to uncon-trollable levels. To prevent this happen-ing, fit wire links 2-3 and 4-5 to keep the4047 operating in the astable mode. Con-nect pin 2 of the timebase circuit (100 Hzsignal) to pin 3 of the 4047 via a 10 !alresistor. Remove Ri and CI from the mainconverter board.

Attention: none of the above changesapplies to the free -running version of thepower converter.

CORRECTIONS

Simple AC millivolt meterJanuary 1990, p. 22-25

In the circuit diagram, Fig. 1, the voltageshown at the base of TS is measured withrespect to the positive supply rail.

Dark -room clockFebruary 1990, p. 62-66

The value of R17 (1 k.(2) is best increased to10 kfl to prevent Ts overloading the Q13output of ICI, which may cause erroneousclocking of ICI.

In Fig. 4, pin 9 of ICI should also becircled to indicate that a through -contact

wire must be fitted in the relevant PCBhole.

Vocal eliminatorJuly/August 1989, supplement p. 5-6

Pins 5 (+input) and pin 6 (-input) ofopamp A2 must be transposed in the cir-cuit diagram.

Voice recorder from TexasInstrumentsJune 1989, p. 43-45The supply voltage pin numbers of IC2,IC3 and IC4 are given incorrectly in thecircuit diagram in Fig 6.

Pins 18 of IC2 and IC3, and pin 4 of IC4,must be connected to ground. Pins 9 of IC2and IC3, and pin 8 of IC4, must be con-nected to +5 V.


SURGE SUPPRESSORJ. Ruffell

It is an annoying but generally accepted fact that muchmains -operated equipment produces surges and other interference

on the mains. But we do not have to put up with clicking noises fromAF equipment as the refrigerator switches on, or a computer that

stops working when the lights are switched on. All that is needed toprevent these irritating effects is a good -quality mains filter.

Cut

SUBGEpLuG

(3

Ideally, any mains outlet supplies an al-ternating voltage of a root -mean -square(rms) value and a frequency specified bythe national (or local) electricity supplier(in the larger part of the UK, these valuesare 240 Vrms and 50 Hz respectively). Inpractice, however, this is hardly ever so.In not a few cases, the mains voltage isoccasionally corrupted by high -frequencysignals, data -bursts, brief fluctuations,surges and dips.

Although. mains signalling is a well-defined area, some types of mains inter -corn operating at carrier frequencies of100 kHz and up are notorious sources ofinterference. Pulse -like interference oftenemanates from dimmer circuits, switch -mode power supplies in computers anddefective or poorly decoupled householdequipment like coffee machines and re-frigerators.

In some countries, the electricity sup-pliers themselves use the mains lines toconvey control information for nor-mal/reduced rate switching of domesticpower consumption meters.

To avoid problems with any equip-ment powered from the mains, a mainsfilter as the one described here must workin both directions, which means that bothmains -borne interference and interferencegenerated by the equipment must be sup-pressed. The filter proposed here is suit-

pO\NE

able for use with 220-240 V mains systemsoperating at 30 Hz.

Design considerationsThe mains filter is basically a passive low-pass with a roll -off frequency of 50 Hz. Itslikeness to a low-pass filter for audio ap-plications is only superficial howeversince the high operating voltage and theassociated considerations as regardssafety govern the use of special compo-nents. In many countries, standards havebeen set up that define the maximum ca-pacitor values used in the filter, often de-pending on whether mains -poweredequipment is wall- or floor -mounted, orportable. These capacitor values are acarefully established compromise be-tween acceptable switch -on and switch -off currents on the one hand, and the riskof electrical shock in the case of defectiveor improperly connected earthing on theother.

Capacitors alone can not secure the re-quired slope steepness of the filter. Theattenuation outside the pass -band is im-proved considerably by using one or morechokes. These come in at least three ver-sions. In general, the choke with the hig-hest inductance is the most effective.However, if reactive loads are powered,the voltage drop across the choke rises

with inductance. In practice, this meansthat the filter has to be geared accuratelyto the load and the nature of the antici-pated interference.

The simplest version is the saturationchoke. When the mains is switched on,this type of inductor possesses a high in-ductance, which rapidly becomes smalleras the current causes the ferrite -iron coreto become saturated. The interferencesuppression grade is nearly always speci-fied for symmetrical (balanced) inter-ference, that is, interference that existsbetween the live (L) and neutral (N) line.

The multiple -winding current -com-pensated toroid choke is more effectivebut also more expensive than the satura-tion type. Strong capacitive coupling be-tween the circuit and the enclosure causesan asymmetrical current (between L/Nand E) to flow into the equipment throughthe earth wire, and half of it back into themains through the live or neutral line. Thepartial interference current causes thechoke, of which the windings are insertedin the phase or neutral line, to be dampedso that the magnetic fields generated inthe windings cancel one another. The in-ductance of both chokes is small for theload current and therefore introduces asmall voltage drop only.

The bar -type choke is best used forloads over 100 A that produce mainlysymmetrical interference (between liveand neutral). In contrast to the saturationchoke, the inductance of a bar -type chokeremains constant.

Practical circuitThe circuit diagram of the mains filter isgiven in Fig. 1. The mains voltage is ap-plied via connector Ki. Components Ciand R2 form a potential divider for theon/off indicator, Di. Capacitor Ci dis-

Mains signaling in the UK is subject to theprovisions of British Standard BS6839. Fur-ther information on the subject may be ob-tained from BIMSA (BEAMA Interactive andMains Systems Association), LeicesterHouse, 8 Leicester Street, LONDON WC2H7BN. Telephone: (01-437) 0678.

ELEKT OR ELECTRONICS MARCH 1990

GENERAL INTEREST 45charges via resistor RI when the filter isdisconnected from the mains. Diode D2 isconnected across Di to keep the reversevoltage across the LED within safe limits.Voltage peaks exceeding 230 V are elimi-nated by varistor VDRi.

Capacitors C2 and C3 must be class -X2types. Similarly, C4 and Cr, must be class -Ytypes. These type codes indicate an a.c.working voltage of 250 V and apply tometallized polyester or polypropylene ca-pacitors with good self -healing propertiesshould arcing occur in the dielectric ma-terial. X2 -class capacitors may not be usedin positions where their failure would ex-pose anybody to electric shock. Conse-quently, these capacitors are connectedbetween the live and neutral lines to en-sure that failure can only cause a blownfuse (in the case of a short-circuit) or re-duced filter operation (in the case of anopen -circuit). Both effects are annoyingbut not dangerous.

The requirements of the Y -type capaci-tors, C4 and C5, are more stringent (seeB.S. 6201, part 3, and IEC 161). Like C2 and Fig. 1. Circuit diagram of the surge suppressor.

Fig. 2. Track lay -out (mirror image) and component mounting plan of the printed -circuit board for the mains filter.

COMPONENTS LIST

Resistors:Ri =IMO 0.33 WR2 = 3k3 0.33 WR3 = 330k 0.33 WVDRI = S10K250

Capacitors:Cr = 150n: 630 VDCC2:C3 = 470n: 250 VAC class -X2 2

G4;C5 = 2n2; 250 VAC class -Y 3

Semiconductors:Di = LED 5 mm redD2 = 1N4007

Miscellaneous:= choke 2x10 mH Type RD62-3 or

2x4 mH type RD 62-6 4.

Ft = fuse 2.5 A slow (for RD62-3) or 5 Aslow (for RD62-6).Ki ;K2 = 3 -way PCB screw terminal block(pin distance 10 mm).ABS enclosure 110:110x65 mm.Panel -mount mains socket with integral fuse -holder.Panel -mount mains receptacle.PCB Type 900016 (not available throughthe Readers Services).

ElectroValue Limited 28 St Judes Road Englefield Green Egham Surrey TW20OHB. Telephone: (0784) 33603. Telex:264475. Fax: (0784) 35216. Northernbranch: 680 Burnage Lane ManchesterM19 1NA. Telephone: (061 432) 4945.

2 e.g., RS Components stock no. 115-219.3 e.g., RS Components stock no. 114-496.

4 Schaffner UK Headley Park Area 10 Headley Road East Woodley READINGRG5 4 -SW. Telephone: (0734) 697179.

ELEETOR ELECTRONICS MARCH 1990

46 SURGE SUPPRESSOR

C3, they cause degraded filter operation inthe case of open -circuit failure. More im-portantly, however, a short-circuit ineither C4 or Cs causes the live (L) or neu-tral (N) line to be connected to the protec-tive earth line. Hence the followingwarning:

Never use capacitors of a different typeor rating than those indicated.

The inductance in the filter is formed by acurrent -compensated choke. The printed -circuit board allows two different typesfrom Schaffner to be fitted. These typesdiffer in respect of maximum load currentand inductance. The 2x10 mH inductorType RD62-3 is rated for up to 3 A, and the2x4 mH Type RD62-6 for up to 6 A.

ConstructionFor reasons of safety, the mains filter mustnot be constructed on any other boardthan that shown in Fig. 2. Construction isstraightforward with the possible excep-tion of Li, of which the mounting dependson the type used. The larger and moreexpensive 6-A inductor is fitted upside-down on the PCB. The underside of thechoke has four colour -marked wires. Thetwo dark -coloured wires are the inputconnections (at the side of C2 in the circuitdiagram). The two light-coloured wiresare the output connections (at the side of

Digitrap-2 CD filterSage Audio have recently introduced twotypes of passive filter that are claimed toeliminate residual quantization noise atthe signal outputs of CD players. Thisnoise occurs typically at the sampling fre-quency (44.1 kHz) and harmonics thereof.A sample of the Digitrap-2 version wastested in the Elektor Electronics engineer-ing department with some interesting re-sults. The filter was inserted between aswept frequency generator and a signallevel recorder. The result of the first test isshown in Fig. 1. The response is virtuallystraight to 10 kHz, but then rises to a peakof about +4 dB at 33 kHz. The claimedattenuation of 30 dB at 44.1 KHz was,however, about correct. The measured re-sponse could not be improved by varyingthe filter load impedance between 600 Qand 1 MQ. The source impedance, how-ever, appeared to be the cause of the un-wanted peak. When changed from about10 Q to 470 0, the response curve becamestraight within 0.1 dB, the peak at 33 kHzdisappeared, and the attenuation at44.1 kHz was 30 dB as before. Figure 2shows the results. The phase shift was alsomeasured and found to be quite smoothwell up to 20 kHz. In all, the Digitrap-2 isa well -designed and correctly working AFfilter when connected to the right sourceimpedance.

Next, the Digitrap-2 was subjected to asubjective listening test by connecting it to

Cs in the circuit diagram). The photo-graph in Fig. 3 shows the RD62-6 on thecompleted board.

The smaller 3-A inductor Type RD62-3is fitted in the normal manner with theconnections inserted direct into the rele-vant PCB holes.

Do not test the mains filter before it is

fitted into the relevant equipment, or -ifit is to be used for various appliances-into a separate ABS enclosure without anymetal part. The prototype shown in theintroductory photograph has a mainssocket and a mains plug for panel mount-ing as used on personal computers.

NEW PRODUCTS

a CD player with 8 -times oversampling.The loudspeakers used were electrostatictypes for the high and middle ranges. Inthis high -end equipment configuration,the Digitrap-2 had a small, but definitelynoticeable, effect: it made the overallsound a little smoother. Whether or notthis is desirable is, obviously, a matter of

personal taste, but it also depends on thequality of the available audio equipment.

In conclusion, the Digitrap-2 is recom-mended to users of CD players who wantto get the most out of their high -end audioequipment configuration. Care should betaken, however, not to connect the filter toa CD player with an output impedancesmaller than 200 0.

More information on the Digitrapseries may be obtained fromSage Audio Electronics ConstructionHouse BINGLEY BD16 4JH.


AUDIO/VIDEO MODAATOn

potadii/310r

,E0 100°v.000

Many inexpensive or older TV sets lack a SCART or other compositevideo input, and can only be connected to a video recorder or otherequipment via an RF modulator. The modulator described here -adesign by ELV- operates at a UHF TV channel between 30 and 40.Use is made of low cost

excellent sound and picture quality.

TV sets that lack an external video inputare still manufactured and sold in largenumbers. In many cases, these sets arerelatively inexpensive types manufac-tured in Far Eastern countries. Unfortu-nately, upgrading such a TV set with anexternal video input is not possible ingeneral because the chassis is at mainspotential. Not a few owners of a low-costTV set are therefore faced with connectionproblems if the set is to function as a dis-play for, say, a computer that has a com-posite video output but lacks an RFmodulator.

The present modulator covers the fre-quency range from 545 MHz to 625 MHz,which corresponds roughly to UHF TVchannels 30 to 40. The circuit consists oftwo parts:a modulated RF oscillator in a small metalbox;a motherboard on to which the RF oscilla-tor, the SCART socket and the supply volt-age regulator are fitted.

The motherboard and the RF oscillatorform a compact unit fitted in an ELVMicroline enclosure as shown on theabove photograph. The modulator ispowered by an external mains adapterwith an output voltage of 12-15 V at about250 mA.

Since the RF oscillator is a separate mo-

MAIN SPECIFICATIONS

High output level: approx. 100 mV(80 dBpV)

Good frequency stability

Low spurious radiation

Audio -video input with SCART socket

Adjustable sound subcarrier frequency

Suitable for upgrading existing equip-ment

dule in the modulator, it may be usedwithout the motherboard to upgradeexisting video equipment with a TV out-put.

The circuitThe circuit diagram of the RF oscillatorwith modulation input is given in Fig. 1.The heart of the circuit is formed by ICi, aType TDA5660P single -chip multi -stand-ard VHF/UHF audio/video modulatorfrom Siemens.

The amplitude of the sound signal ap-plied to pin 6 of the SCARTsocket, Bui, isset with P1. Note that the SCART socketand the preset are not contained in theRF-tight metal enclosure. The sound sig-

nal is capacitively fed to the FM (fre-quency -modulation) sound input of theTDA5660P via C1 -C2 -R2. Components R2 -C2 -R3 form a pre -emphasis network. Thefrequency -modulated sound subcarrier isadded to the vision signal by the RF mixerin the TDA5660P.

The sound subcarrier frequency (UK:+6.0 MHz) is set by a parallel tuned cir-cuit, L1 -C14. The vision -to -sound carrierratio of 12.5 dB is ensured by R9. Capaci-tor C22 connects the AM (amplitude -modulation) sound input of theTDA5660P to ground for alternating volt-ages.

The CVBS (chroma-video-blanking-sync) signal taken from pin 20 of theSCART socket is terminated into Rif andcapacitively fed to video input pin 10 ofthe modulator chip via Cis. A clampingcircuit at this input establishes a fixedsynchronization level, while an automaticgain control circuit that acts on the peakwhite values compensates amplitudechanges of up to 6 dB. Both the clampingcircuit and the gain control circuit are in-ternal to the TDA5660P. Capacitor C:7 fil-ters the current pulses produced by thepeak white detector, and its value deter-mines the time constant of the gain con-trol.

The modulation index of theAM visionsignal is set by the potential at pin 12 of



the TDA5660P. If no resistor is connectedto this pin, the modulation index is 0.8(8091) for negative video modulation.Note that pins 12 and 2 (reference voltage)are decoupled to ground to prevent inter-ference.

The symmetrical oscillator on boardthe TDA5660P is bonded out to pins 3-7.The external tuned circuit is formed byinductor L3 in combination with capaci-tors C4 and Cio, and variable capacitancediode Di. Capacitors Cs and Cu preventthe direct voltages at pins 3 and 11 beingshort-circuited via L7. The oscillator has aseparate ground connection bonded outto pin 5.

The anode of varicap DI is groundedfor direct voltages by R4. The oscillatorfrequency is adjusted with the aid of atuning voltage supplied by preset 126 andapplied to Di via Rs. Capacitors C and Cudecouple the RF voltage generated by theoscillator.

The modulated RF signal (AM visionand FM sound) is taken from the outputsof the balanced mixer in the TDA5660P viapins 13 and 15. The output impedance of300 U balanced is transformed down to75 U unbalanced by L2, a Guanella trans-former, perhaps better known as a balun.Capacitor Clb, finally, feeds the modu-lated UHF signal to the RF output socketvia terminal ST6.

The modulated RF oscillator ispowered by a regulated voltage of 10 V. A12-V supply may also be used in case theoscillator is incorporated into existingequipment. The output voltage must,however, be regulated.

The motherboard has on it the RF oscil-lator module, the SCART socket, But, thesound level control, Ri, and the 10-V regu-lated power supply. The circuit diagramof the latter unit is shown in Fig. 3. Theunregulated voltage applied to socket Butmay lie between 14 V and 17 V. The cur-rent consumption of the modulator is lessthan 50 mA, so that a small mains adaptermay be used.

The power supply itself is a standarddesign based on a three -pin fixed voltageregulator Type 7810 (1C2). LED D3 func-tions as an on/off indicator. The mini-mum and maximum voltage that may beapplied to Bu: is 12.7 V and 25 V respec-tively.

ConstructionThe main point to note about the construc-tion of the modulator is that the RF oscil-lator must be thoroughly screened toensure mechanical as well as electrical sta-bility and at the same time prevent spuri-ous radiation of the UHF signal.

Start the construction by populatingthe oscillator board: fit and solder the twowire links, the six resistors and the vari-cap. Next, fit the capacitors, making surethat the ceramic types are pushed as far aspossible towards the PCB surface. Fitpreset R6 and inductors Li and U. Do notfit the balun the wrong way around: theconnection that consists of four joined

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wires goes to Cu. Finally, fit the IDA5660.Do not use an IC socket.

Inductor L3 is made by winding 2 turnsof silver-plated wire around a 3 -mm drillor pencil. Take the inductor from the for-mer and space its turns evenly by about2 mm. Insert its terminals into the relevantPCB holes and push it as close as possibleto the PCB surface. Solder the terminals atthe track side.

Finally, fit four solder terminals at thetrack side of the board, and one solderterminal (ST6) at the component side.

Bend the strip of tin-plate screeningsupplied with the kit at the indicatedplaces to form a box. Join the ends bysoldering. Fit the oscillator board into thebox and ensure that the track side is about3 mm above the lower edge of the tin-plate box. Solder the board to the inside ofthe box at all four sides. Work quickly toprevent overheating, and use a high -power (50-W) solder iron to ensure asmooth and firm connection.

Mount a narrow strip of tin-plate ver-tically between the two rows of IC pins atthe track side of the board as shown in thephotograph in Fig. 4. Like the box, thisstrip is soldered over its entire length.

Insert the panel -mount TV plug intothe side panel hole, and secure it by solde-ring. Use a short length of light -duty wireto connect the centre pin of the plug toterminal ST6.

Proceed with the population of themotherboard, which contains few partsonly. LED D3 is soldered to terminals ST11and STI2. Four additional solder terminalsare fitted to enable the sides of the RFoscillator box to be secured later.

Inspect the two boards for short-cir-cuits and bad solder joints, and correctany errors if necessary. Mount the bottom

section based on the TDA5660P.

cover on to the oscillator box, making surethat it does not touch any of the foursolder pins which should be about centralin the holes provided in the cover. Solderthe bottom cover to the sides of the box.

Place the oscillator box on the mother-board and insert the four terminals intotheir respective holes. Solder them at thetrack side of the board. Next, solder thefour terminals on the motherboard to thesides of the oscillator box.

AdjustmentThe adjustment of the modulator is rela-tively simple and does not require specialtest equipment.

Connect the modulator to the videosource, the TV set and the mains adapter.Tune the TV to a free channel between 30and 40. Adjust RI until the remodulator istuned to the TV channel. The tuning rangeof the preset should cover the UHF rangebetween channels 30 and 40. Ii this is notso, carefully stretch or compress the turnsof L3 until the required range is covered.

Next, adjust the sound channel. Turn

Fig. 2. Circuit diagram of the 10-V regu-lated power supply.

ELERTOR ELECTRONICS )1ARcH t99(1

%UM() VIDEO SIODULAToR 49the core in Li until the sound on the TV setis clear and undistorted.

If the modulator works to your satis-faction, mount the top cover on the oscil-lator box, and secure it by soldering. Next,place the complete assembly into the ABSi`licroline enclosure. The printed and pre -drilled front -panel supplied with the kit isfitted last by pressing it firmly from oneside so that it clicks into the enclosure. si

COMPONENTS LIST

Resistors:880.

R12 = 11(0R9 = 6k8R2:133= 22k114;Rs = 47kRe = 5k0 preset V

Ri = 10k preset V

Capacitors:Cc:C7;Ce = 1p5

2p2C4:ClG = 6p8C14= 100pC2 = 220pC13;C22 = 820pCIE = 1110

C3:Cie = 10nC9:C12 = 22n: ceramicC2C.: = 47n

= 470nC17;C2i = 10g; 16 VC19 = 470p: 25 V

Semiconductors:IC = TDA5660PIC2= 7810Di = B8505E1 = 1N4001D3 = LED: 3 mm: red

Miscellaneous:L. = 10pH.1_2 = balun.But = SCART socket for PCB mounting.But = jack socket for PCB mounting.Sti = fuse: 125 mA.Qty. 1: tin-plate box (complete).Qty. 1: TV coax ;Ala.Qty. 1: PCB -mount fuse holder.Qty. 11: solder pin.85 mm light -duty wire.

A complete kit of parts for theaudio/ video modulator is availablefrom the designers' exclusive world-wide distributors (regrettably not inthe USA and Canada):

ELV FranceB.P. 40F-57480 Sierck-les-BainsFRANCETelephone: +33 82837213Fax: -*33 82838180

Also see ELV France's advertisementelsewhere in this issue.

Below: completed RF oscillator module seenfrom the PCB track side. Note the screenfitted vertically in between the pin rows ofthe dual-indine integrated circuit. Thisscreen is essential to keep spurious radia-tion of the modulator to a minimum.Right: top view of the completed RF modu-lator assembly. The RF oscillator box ismounted on to the main board. Note that thetop cover has been removed for an internalview of the oscillator.

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ELENTOR ELECTRONICS MARCH 1990

50

TECH\O,OGYRESEARCH AND DEVELOPMENT:

KEYNOTE OF CLUB LIFE AT HARWELL

by H. Cole, CEng, MIERE, Senior scientist at Harwell Laboratory

Harwell Laboratory. situated about 50 miles tothe west of London. is the largest United King-dom Atomic Energy Authority (L:KAEA) re-search establishment. It has an annual turnoverin the region of £140 million and employs4250 people. The laboratory was set up in 1946to carry out research into all aspects of atomicenergy and furnish the scientific and technicalinformation needed for Britain to embark on anuclear power programme. The result of thisearly work culminated in the commissioning in1956 of Britain's first nuclear power station: a200 MW plant that is still feeding power intothe national grid.

Today there are 17 nuclear power stationsoperating in Britain and one I a pressurizedwater reactor-gwK) is under construction. To-gether. these satisfy about 20% of the country'selectricity demand.

Since 1965. the laboratory has undertakenan increasing amount of work that is uncon-nected with nuclear research and, althoughthere is still a substantial nuclear programme,this now accounts for little more than half ofthe financial turnover.

The non-nuclear work involves liaison witha wide sector of industry and commerce andranges in scope from the neutron radiographicexamination of jet engine turbine blades to theultrasonic inspection of hundreds of miles ofrail track and consumer gas distribution pipe-lines. Clients range from small private compa-nies to giant multinationals: contract valuescan be as little as hundreds of pounds or asgreat as several millions.

Cost sharingThe ever increasing complexity of present daytechnologies and the need for innovation andthe development of new materials and pro-cesses have demanded facilities that are oftenbeyond the financial and material resources ofall but very large organizations: hence the needfor a research establishment like Harwell.Clients may visit the laboratory and hire the fa-cilities and scientific back-up for as long asthey wish without having to embark upon ex-pensive in-house alternatives. They can alsojoin one of the many cost -sharing research anddevelopment clubs that are operated by the lab-oratory.

Hanvell's first club, the Heat Transfer andFluid Flow Service (HTFS) was set up in 1968and is operated jointly with the National Engi-neering Laboratory and, since 1983. with

Atomic Energy of Canada Limited. Other clubswere added during the 1970s but growth intheir numbers began in earnest during the1980s as industry began to emerge from the in-ternational recession.

Harwell now operates a total of 30 clubscovering. a wide spectrum of industrial technol-ogy and the number is growing by about twoever year.

Club -funded research and developmentprogrammes give members the advantage, fora relatively modest outlay, of sharing the bene-

An example of a failed high strength marine boltexamined by the Offshore Bolting Materials Club

of Harwell Laboratory.

fits accruing from a particular project whilemaintaining confidentiality with regard to po-tential (non -club) competitors.

Multinational membershipThere are essentially two types of Harwell clubactivity. The first is basic research with no ob-viously exploitable end product in mind butwhich may provide valuable background infor-mation for subsequent commercially viable de-velopment programmes. Examples of this in-clude materials evaluation programmes forsolid-state eas sensors and the development oftechniques for studying combustion behaviourin advanced petrol engines.

The second kind of club activity is the de-velopment of technology to support a compa-ny's activities on a wider scale than would betackled in-house. It is this area of work thatcalls upon the special skills and facilities ofHamel!. Examples include the formulation ofoffshore inspection techniques and associatedinstrumentation, and of an inspection systemfor composite materials.

The detailed structure and operation of thevarious clubs varies considerably to suit theirparticular activities. Some larger clubs mayhave nearly 200 members, whereas the smaller,more specialized, ones may have about ten.The work undertaken by a club may be con-fined to a particular type of industry, such asoffshore inspection, whereas other morebroadly based clubs may span a wide range ofindustries. The Composite Metal Jointing Club.for instance, has a membership drawn from theaerospace. automobile. adhesive and compos-ites manufacturing industries.

Clubs with a multinational membership at-tract financial support from the European Com-munity and cover research and developmentthat is advantageous to member states. Typicalof the many internationally funded ones is theResidual Fuel Oils Club. which studies thecombustion characteristics of low -qualityresidual fuel oils. Membership fees generallyrange from about £5,000 to £15,000 per yearbut can be much higher. Some club fees are de-pendent on company turnover and are gener-ally larger for overseas organizations. Forsmall British companies. the fees are usually inthe region of £3.000 a year.

Guided by membersMost club projects are of limited duration andare organized into phases. the results from onephase determining the direction and extent ofthe next. Some clubs, like the Diesel EngineWorking Party. have successfully completedtheir programmes and ceased operation. Oth-ers. such as FrrFs. have rolling programmes thatare regularly redirected along lines that reflectthe current priorities of their members.

For many clubs, support funding from theBritish Government or from the EuropeanCommunity often approximates to that of themember's contribution. For some clubs. how-ever, less government funding may be forth-coming and be limited to a simple membershipcontribution fee. This applies in the case of theOffshore Inspection Service Club whose only


RESEARCH & DEVELOPMENT: KEYNOTE OF CLUB LIFE AT HARWELL

form of government funding is a single mem-bership fee.

In spite of these differences in funding andcomposition, one strong common featureamong the Harwell clubs is that the work un-dertaken is guided by the members and reflectstheir priorities. providing a firm base for thesubsequent transfer of the resulting technology.

The Biotechnical Separations (BiosEP) Clubprovides consultancy, design and reports andcarries out basic and applied research on all as-pects of downstream processing for the

biotechnology industry. Membership is drawnfrom chemical. pharmaceutical and food pro-cessing companies, and others with specialistmedical and biotechnology interests.

Another club, Composite Metal Jointing.provides design criteria and design tools anddata required for load -carrying adhesive jointsbetween polymer -based composites and met-als. The membership includes European auto-motive and component manufacturers.aerospace companies and adhesive and compo-nent suppliers.

World-wide membership

Heat Transfer and Fluid Flow Service (HM-rst.

the oldest Harwell club, has over 185 mem-bers. Collaborators are the National Engineer-ing Laboratory and Atomic Energy of Canada.It provides computer programs. design reports.literature digests. consultancy and access to alarge international research and developmentprogramme on heat transfer and fluid flow. Thesubstantial world-wide membership includeslarge chemical and petrochemical companies.process plant contractors and small heat ex-changer manufacturers.

The Fouling Forum has over 200 membersand works in collaboration with the NationalEngineering Laboratory. It provides a forumfor the interchange of ideas and for technologytransfer on the subject of fouling of heat ex-change services in a wide range of processplant. Membership of this low-cost informationexchange club includes all HFTS members andis also open to other subscribers.

The Metal Matrix Composites Club is con-cerned with research and development into theproperties of, and processing methods for, alu-minium alloys reinforced with ceramic andother fibres as well as processing routes forspecific components. Membership covers sev-eral industries and includes aerospace. automo-bile and component manufacturers and materi-als suppliers.

Metals and enginesThe Midas Club provides a service for the min-erals exploration production and processing in-dustries. It develops new or improved analyti-cal methods for interpreting data from neutronand gamma ray -based interrogation probes asused by the oil, gas, coal and metalliferousminerals industries. The members includemajor oil companies and their contractors plusa number of coal mining companies and their

customers.Offshore Inspection Research and Develop-

ment Service produces new or improved in-spection techniques for offshore structures. Thecurrent programme includes work on ultrasonictime -of -flight and eddy current inspectionmethods and a project on the detection of tightcracks. The membership is drawn from themajor offshore operating and inspection com-panies.

Offshore Bolting Materials is a small cluboperated in collaboration with \Vimpey Labo-ratories. It develops improved bolts and boltingmaterials for use on offshore structures. Itsmembers come from the major oil companiesand safety authorities.

The Petrol Engine Working Party appliesthe Harwell -developed laser -Doppler anemom-etry and CARS t coherent anti -Stokes Ramanspectroscopy ) techniques and associated instru-mentation to studies of air flow and combus-tion within operating internal combustionpetrol engines. Its members are drawn from en-gine and component manufacturers and a fuelsupply company.

Fuel efficiencySupported by Britain's Department of Tradeand Industry and the European Community. thePlasma Etching Club undertakes collaborativeprogrammes for devising techniques for the dryprocessing of very large-scale integrated cir-cuitry. The work involves the formulation ofsilicon -based devices and different aspects ofetchant chemistry. The members of this clubare suppliers of high -purity chemicals andgases and of specialized processing equipment.

Positron annihilation is a non-destructivetesting (NDT) technique developed at the Na-tional NDT Centre at Harwell. It relies on theemission of positrons (positively charged elec-trons) from a small radioactive source and theinjection of these particles into the object beingexamined. The positrons. on entering the ob-ject. are quickly annihilated by the more nu-merous negatively charged electroncs and giverise to a pair of gamma rays. each of 0.51 MeVkinetic energy and travelling in opposite direc-tions. for each annihilation event.

The detection of these gamma rays fromdifferent directions can indicate the presence ofdefects in the object being examined. show theonset of fatigue in metals and alloys. or enablethe moisture content of resin composites to bedetermined.

The Positron Annihilation Club in% estigatesthe application of this novel technique and itsmembers are drawn mostly from the aerospaceindustry.

The Residual Fuel Oils Consortium studiesthe application of laser -based instruments andassociated analytical facilities to the combus-tion characteristics of low -quality residualfuels-such as those used in marine and indus-trial type engines-to see if they can be burnedmore efficiently. This is an international con-sortium involving medium -speed diesel enginemanufacturers, a component manufacturer. an

oil company and representatives of the ship-ping industry.

Improving batteries

Separation Process Service isest is a collabora-tive club operated with the government's War-ren Spring Laboratory of Stevenage. It pro-vides reports. consultancy and access to a largeresearch and development programme in fiveseparation process areas: solids drying; gascleaning; solid -liquid and liquid -separation;and crystallization. Membership covers a widespectrum of process plant users, contractorsand manufacturers.

The Solid State Battery Club carries out re-search into solid-state rechargeable lithium bat-teries with the aim of developing the technol-ogy required for safe. rugged, light -weight ver-sions suitable for products ranging from powertools and portable consumer products to vehic-ular traction. The wide-ranging membershiprepresents battery manufacturers. companieswith facilities and expertise in the methodslikely to be required in battery construction,and potential users of the final product.

Eliminating microchip errorsA new. collaborative research project aimed

at impro% in2 the quality. reliability and perfor-mance of semiconductor devices. the Soft Er-rors Club, was launched recently by Hanvell'sMicro -electronic Materials Centre.

The membership brings together leadingUnited Kingdom semiconductor manufactur-ers, users. materials suppliers and scientistswith the objective of dramatical reducing theproblem known as 'soft errors' in micro -elec-tronic circuits.

Soft errors, more properly called single -event upsets. are caused by alpha particlesemitted by naturally occurring radioactive im-purities in the materials used to make inte-grated circuits. The alpha particles carry suffi-cient electrical charge to alter the contents ofmemory cells. thereby causing computationalerrors. The more closely packed the memorycell, the greater is the risk of single -event up-sets.

The research programme will extend thetechnique developed at Harwell. known as fis-sion track autoradiography (FrA). This makesuse of optical microscopy to count the numberof fission tracks that have occurred in a thinpolyamide film coating on a semiconductorspecimen that has been irradiated by neutronsderived from a nuclear reactor. This techniquealone is capable of detecting the presence ofuranium impurity atoms at concentrations aslow as two parts per million.

The Soft Errors Club is essentially a two-year programme and has the financial supportof the British companies MEDL. tNMOS. Ana -manic and Britain's Department of Trade andIndustry. The club remains open to UnitedKingdom organizations and overseas compa-nies that have a significant manufacturing pres-ence in Britain.


THE DIGITAL MODEL TRAINPART 12 ADDRESS DISPLAY

by T. Wig -more

The address display is a small extension unit that is used inconjunction with the mother board. It indicates to what locomotive

address a given controller is set and whether a givenlocomotive controller is active.

The address display, which may befitted to each and every locomo-tive controller, improves the easeof operation of the system. It is notstrictly essential, but will be foundvery useful with concentratedmulti -train operation.

If addresses in the locomotivecontrollers have been set via theRS232 interface, that is, not byhardware, it is convenient if theaddress setting is displayed to in-dicate that it has been set correctly.

Furthermore, the address dis-play indicates whether a given lo-comotive controller is active.When a controller is taken out ofaction or when the control of therelevant locomotive is taken overby the serial interface, the corre-sponding address display isquenched, except in one condition.When the system is in the stopmode and a locomotive address isset via the RS232 interface, the dis-play will indicate that address al-though the controller is inactive.

Because of this arrangement,addresses may be set in the con-trollers via the RS232 interface andchecked while the system is still inthe stop mode. When the systemis then actuated, the displays of allnon -active controllers will go out.

A controller is not active if:

it is not connected to themother board;the operating switches are inposition "out of action" (highimpedance at pins 4 and 5 ofthe DIN connector);a controller with higher priorityhas been set to the sameaddress;the locomotive with the rele-vant address is given a controlinstruction via the RS232 interface.

The last condition needs ampli-fication. Any control instructionsto locomotives via the RS232 inter-face will deactuate the controllers

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that serve the locomotives with thesame address. The control of anylocomotive that is operated via theRS232 interface may be reverted tomanual by the locomotive enablecommand <37>. When this instruc-tion is given, the display of the as-sociated controller will light again.

Circuit descriptionAs is clear from Fig.79, the circuitof the address display is simplicityitself, because the control is pro-vided by the mother board.

The circuit proper consists of twoBCD -to -7 -segment decoders withintegral register and the displays.

The decoders are connected tothe identically -named locomotiveaddress bus on the mother boardvia lines LAO-LA7 (LA = locomo-tive address).

Line Sn carries the selection sig-nal that becomes active as soon as agiven controller is selected. The se-lection causes a certain locomotiveaddress set by hardware to be readand then to be written into the reg-isters of the BCD -to -7 -segment de-coders.

If there is no controller con-nected, the display is quenched atonce by the system writing FFH toit. The display is also quenched ifthe system signals a controller withhigher priority, that is, a highercontroller number, which is set tothe same address or if the locomo-tive with the associated address iscontrolled via the serial interface.

If no address has been set byhardware, the system verifieswhether an address for the relevantcontroller has been given via theRS232 interface. If so, the addressthat has been converted to BCDformat is sent to the display circuit.It is for this reason that the bufferfor reading the locomotive address(ICI on the mother board) must bea bidirectional type.


THE DIGITAL MODEL TRAIN - PART 12: ADDRESS DISPLAY

Fig. 80. The printed circuit board is designed for building up to four address display units.

Fig. 81. Construction of the boards as a sandwich: 81a - the decoupling capacitor is laid slat on the board:81b - through connexions are made with the aid of the resistors: 81c - the power lines are looped through:

81d - the sandwich is ready for connexion to the mother board.

PARTS LIST

R1 -R14 = 660R (small types)

Cl = 47 n (preferably SMA type)

IC1, IC2 = 4543 (SMA type)

LD1. LD2 = HD1105 (red)

PCB 87291-9

ConstructionThe construction of the display in-volves some rather fiddly work, be-cause to keep the unit small, thecomponents should, if at all possi-ble, be very small or of the SMA(surface mount assembly) type. Inthe case of the ICs, there is nochoice: they must be SMA types.

The boards are not wider thanthe displays to enable a number ofunits to be mounted side by side(unless only one locomotive con-troller is used, of course).

Furthermore, the most conve-nient type of construction is thesandwich type in which the resist-sors are used for making the neces-sary connexions.

The printed -circuit board inFig. 80 allows up to four displayunits to be constructed. The motherboard can handle up to 16 displays,so that if the maximum is chosenfour PCBs are required.

Before the construction propercan be started, the board must becut (lengthwise) into two identicalstrips if four adjacent units arewanted or into eight parts if fourdiscrete units are required. The fol-lowing notes apply to the buildingof one unit only. Some assembly instructions are

given in the caption of Fig. 81. Mount both 7 -segment displayson to the top "wafer".

Fit both right-angle wire links totIenforricopper side of the lower

Mount decoupling capacitor C1 atthe copper side of the upper"wafer". If an SMD type provesunobtainable, use a small ceramictype and mount this as shown inFig. 81a.

Mount ICI and 1C2 at the copperside. Pins 1-8 are located at thebevelled side of the devices.These sides should point to oneanother.

Connect the two wafers togetherwith the aid of the resistors asshown in Fig. Sib. The copperside of each wafer should facedownwards. The resistors shouldbe of the smallest commercialtype to ensure a compact unit.

Loop the power lines in betweenthe two wafers (top right and un-derneath LD1) with the aid of twoshort lengths of equipment wireas shown in Fig. 81c.

ELENTOR ELECTRONICS MARCH 1990

54 GENERAL INTEREST

0

o

0O

C390-11-0

0000

0000

I oRi- -- R70 r0,,L 1C1Cff

: , g:L, I

C

Re

1.0 - fr-

.

OOOOOOOOO

LO2 L 0 47

1C2- I

011111.

C

EctLM&OKt

XI

5 4 5 4

3 2

K23 2 1

K3

Fig. 82. Showing where connexions from the display unit aremade on the mother board.

InterconnexionsApart from the power lines, there areconnexions between the address displayand the mother board-see Fig. 82.

The power lines (0 V and +5 V) may belooped to other display units via lengthsof normal equipment wire.

Each and every display unit may beused in conjunction with hardware for set-ting the locomotive addresses-see also

PROTECTED QUADPOWER DRIVERS

Providing interface between low-level signalprocessing circuits and power loads, Sprague'sUDN2547B and LIDN2547EB quad powerdrivers combine logic gates and high -currentbipolar outputs with complete output protec-tion.

Each of the four outputs will sink 600 mAin the ON state. The outputs have a minimumbreakdown voltage of 60 V and a sustainingvoltage of 40 V. The inputs are compatible withTTL and 5V CMOS logic systems and includeinternal pull -down resistors to ensure that theoutputs remain OFF when the inputs are open -circuited.

Over -current protection for each channelhas been designed into the devices and is actu-ated at about 1.3 A. It protects each outputfrom short circuits with supply voltages up to25 V. When a maximum driver output currentis reached, that output drive is reduced lin-early, maintaining a constant load current. If

A - supply line earthB - current limiting resistorsC - connexion loc address busD - SMD-type ICE - diodes for loc addressingF - mother boardG - jumperH - DIL switch

Fig. 83. Combination of an address display and hardware for setting locomotiveaddresses.

"locomotive addresses" in Parts 7 and 8. Ifthat is done, it is convenient to removecertain parts to the track side of themother board. Two possibilities are shownin Fig. 83.

In the first (Fig. 83a), the eight diodesare fitted at the track side. The connexionsto the cathodes may be used for connect-ing lines LAO-LA7 to the display unit. Tomake the whole easily removable, the dis-play unit may be provided with a "semi IC

the over -current or short-circuit conditions con-tinue, each channel has an independent thermallimit circuit that will sense the rise in junctiontemperature and turn OFF the individual chan-nel that is at fault. Foldback circuitry decreasesthe output current if excessive voltage is pre-sent across the output and assists in keepingthe device within its SOA (safe operating area).

Each output also includes diagnostics forincreased device protection_ If any output isshorted or opened, the diagnostics can signalthe controlling circuitry through a commonFAULT pin.

The UDN2547B/EB can be used to drivevarious resistive loads including incandescentlamps (without warming or limiting resistors).With the addition of external output clampdiodes, it may be used to drive inductive loads,such as relays, stepping motors, or solenoids.

The UDN2547B is a 16 -lead power DIP,while the UDN2547EB is a 28 -lead powerPLCC for surface -mount applications. Bothpackages are of batwing construction to pro-vide maximum power dissipation over thetemperature range of -20' C to +85' C.

socket". The setting of the loc addressesmay be effected by fixed wire links orjumpers at the track side of the motherboard.

The second design (see Fig. 83b) usesan 8 -pole DIL switch at the track side ofthe mother board for setting the addresses.

Bear in mind that if an address is set byhardware, a locomotive controller can nolonger be allocated an address via the se-rial interface.

HOW TO ORDERTO PLACE AN ORDER. obtain price and deliveryinformation request technical literature or apcbca-bons assistance. contact your local Sprague Semi-conductor sates office or sales representative.

From U.S. Sprague Electric Companyand Semiconductor Group

Canada: 115 Northeast CutoffBox 15036Worcester. MA 01615-0036Tel: (508) 853-5000Fax: (508) 853-5049Ttx: 203658. 221457

From Sprague Electric (U.K.) Ltd.Europe and Semiconductor Group

Mideast. Balfour HouseChurchfieid RoadWalton on ThamesSurrey KT12 2T13. UKTel: (44-932) 253-355Fax: (44932) 248-622Tlx: (851) 926618

From Asia: Sprague Asia Ltd.Semiconductor Group16th Floor. Lap Shun Centre552.556 Castle Peak RoadKwai Chung. N.T., HONG KONGG.P.O. Box 4289HONG KONGTel: (852-0) 428-3188Fax: (852-0) 480.4292

(852-0) 480-5374llx: (780) 43395

ELERTOR ELECTRONICS MARCH 1990

735

AsIC"ST. Giffard

L

Phasing, vibrato and reverberation are commonly used sound effects in modernmusic. The effects unit described here is a high -end piece of audio equipment thatwill make many musicians and sound engineers sit up. Based on a state-of-the-art

bucket -brigade delay (BBD) chip, the unit is capable of many popular sound effects,including ADT, chorus, phasing and real -to -life reverberation.

Under normal circumstances, soundtravels at a speed of about 340 m per sec-ond. This means that short echoes occur inrelatively small rooms already, giving theso-called reverberation effect. Acousticperception experiments have proved thatthe human ear is capable of detecting asound delay as small as 5 ms only (corre-sponding to a distance of about 1.65 m). Inparticular, short reflections with their as-sociated differences in regard of level,delay, and spectral composition create animpression of space with the listener.

Most electronic musical instrumentsare not based on sound created in a reson-ant cavity of any size or shape, and as aresult produce a relatively 'flat' sound.Reverberation may be added by electronicmeans to add warmth to the sound ofthese instruments. In the present soundeffects units, reverberation is achievedwith the aid of adjustable degrees of feed-

back and attenuation, which results in aremarkably natural effect.

Bucket brigade delayThe drawing in Fig. 1 shows the basic set-up of an analogue delay line based on abucket brigade memory. The memory isessentially a series of sample -and -holdcircuits, each of which consists of elec-tronic switches and capacitors. The anal-ogue signals stored in the capacitors aresampled under the control of a centralclock signal. At each clock pulse, thesample is shifted one capacitor to theright, hence the name 'bucket brigade'(the precursor of today's fire brigade).

After a clock pulses, the analogue sig-nal is advanced positions in the mem-ory. A double clock is used to prevent thecontents of two 'buckets' affecting eachother as a result of the shift operation.

1

-

C c

a

:,F_F 4 Ct.:.

Clock 2

=

e"

Bucket Eirip,de 0.-Lce

Fig. 1. Block diagram of the bucket -brigade sound effects unit.

Hence, clock 1 and clock 2 are in oppositephase.

To ensure acceptable distortion of theinput signal as a result of the samplingoperations, the clock frequency must be atleast two times the highest frequency to besampled (Nyquist's sampling theorem). Alow-pass filter at the input of the bucketbrigade delay limits the frequency rangeto a usable value. The output of the BBDchip also has a low-pass filter, in this caseto remove the clock signal component.

ReverberationReverberation is an acoustic effect whichoccurs, in principle, in every room ofwhich the walls have sound reflectingproperties. The sound reflections arenoted by generating a short acousticsound burst, e.g., a hand clap. This soundwill reach the ear directly as well as indi-rectly via reflections. The time it takes anyreflection to reach the ear is in direct pro-portion to the time taken by the sound toreach the point where it is reflected. Theamplitude of the reflection depends on thelength of the path and the acoustic proper-ties of the reflecting surface. Stone walls,for instance, absorb very little sound,whereas curtains have virtually no reflec-tive properties. In many cases, soundreaches the listener via different paths.The amplitude of the reflections as a func-tion of time is illustrated in Fig. 2.

The decay time is the time that lapsesbefore a particular sound is so weak thatit is no longer perceived. This parameterdepends on the construction of the listen-ing room and the materials used. A natu-

ELEKTORELECTRONIC.,; \tAR(H 19911

56 ELECTROPHONICS

ral sounding reverberation effect requiresat least 1,000 reflections per second,which, as a further proviso, must reachthe listener at a certain irregularity.

Reverberation: theelectronic wayFigure 3a shows the simplest configura-tion of a reverberation unit based on con-trolled feedback. The associatedamplitude -vs -time diagram is given inFig. 3b. To achieve a decay effect, the am-plitude of the reflections is reduced as afunction of time with the aid of a voltageattenuator. In practice, the reverberationtime, t, is defined as the time required toreduce the sound energy by a factor of 10-(60 dB). In Fig. 3a, this time may be calcu-lated by counting the number of 'needlepulses' between the instant the sound isgenerated and the instant its amplitudeis 60 dB smaller. Next, the number ofneedles is multiplied with the delaytime, T, of the reverberation unit, hence,

t = 60/at

where a is the attenuation per passage.A practical example: a reverberation

unit has an attenuation of 3 dB and adelay of 50 ms. An attenuation of 60 dBis, therefore, reached after 20 passages,each of which introduces a delay of50 ms. The reverberation time, t, is20x50 ms =1 s.

In practice, reverberation times of theorder of one or two seconds pose prob-lems because they require an extensive(i.e., long) delay line. Acceptable resultsfor reverberation times longer thanabout 0.5 s are only achievable withdigital delay lines. Lower attenuationand a greater number of passes areusually not feasible in view of the risk ofoscillation.

A second problem arises from theequal distances travelled by the gener-ated reflections. Such a constant patterncan only occur in a spherical room, which,in the case of the above example (50 -msdelay time) has a radius of 16.6 m. Evi-dently, such a room is at best rare in thereal world.

An annoying side -effect of equally long treflections is the creation of a comb -filterresponse -see Fig. 3c. At a delay of 20 ms,the distance between two peaks equals100 Hz. The comb filter effect introducesa variation in the attenuation which issimple to calculate if the normal attenua-tion of the circuit is known. From theabove example, a normal attenuation of3 dB means that the signal is attenuatedby a factor of 0.7 after a single passagethrough the reverberation unit. The vari-ation in the attenuation owing to the combfilter effect is (1+0.7)/(1-0.7), i.e., 5.7times or about 15 dB. Obviously, an am-plitude ripple of 15 dB is not acceptablefor hi-fi stereo applications. Yet, manyreverberation units produced in the past

2dB

.E

05m Sound

1.1. cfr<5.

25 75 25 150 1 5lams

Fig. 2. Amplitude -time diagram of a pulseshaped sound and the reflections caused by it.

3

b=g

-6

.421

-16

-241

30-1-

360

C t I1-91

4

20 40 60 60 100 120 140 160 ISO 200 220 240

-O.

Fig. 3. Simplest configuration of a delay line with feedback (3a) and the associatedamplitude -time diagram (3b). The frequency response of such a delay unit is not unlike thatof a comb filter (3c).

4

ar

delay-

delay

6eby7 3

delay, 4

7406

p REM

p

1OZ.1,o

LOg

A2

79:56 -7

Fig. 4. Improved reverberation principle based on individually controlled delay lines.


BBD SOUND EFFEcTs I_ Nit PART 1

Fig. 5. Basic circuits for phasing (5a) andvibrato (5b).

used the above principle simply for lackof a better (electronic) alternative.

Multiple reverberationA naturally sounding reverberation effectcan only be achieved by using differentdelays of non -related durations. The blockdiagram of a reverberation unit based onthis principle is shown in Fig. 4. Frompractical experiments, at least four delaysare required for acceptable results. Thesound effects unit described here has sixdifferent and non -related delays, whilethe attenuation for each of these is ad-justable to give an optimum room simula-tion.

The delays used in the sound effectsunit allow an estimate to be made of thesize of the simulated room. A sound delayof 10 ms corresponds to a total path lengthof 3.3 m, or a wall distance of 1.65 m. Themaximum setting, 100 ms, simulates awall distance of 16.5 m.

Sound effectsThe BBD sound effects unit offers a var-iety of sound effects which may be set toindividual liking with a large number ofcontrols. As examples, the degree of feed-back for the delayed signals may be ad-justed; the 'clean' (input) signal may bemixed with any one delayed signal. Fur-thermore, the unit allows a single delay tobe used.

The ADT-effect (automatic double -tracking) is commonly used in modernmusic technology to give the sound moresubstance. Basically, the signal is brieflydelayed (r=1-5 ms) and then mixed withthe original. If used in a multiple way, theresult is the Chorus -effect. Here, thedelay time is not constant but subject tosmall, irregular changes caused by modu-lation of the clock signal by a pseudo -ran-dom signal generator, for which thesound effects unit has an external input.The chorus -effect may use one or moredelay lines in the unit, provided the out-put signal is not fed back to the input. Thedelayed signal is, therefore, simply addedto the output signal.

Vibrato and phasing are based onmodulation of the clock signal with atriangular, low -frequency, signal sup-plied by, for instance, an LFO (low-fre-quencv oscillator). The vibrato -effect isobtained by using the delayed signal only,while for phasing the modulated as wellas the delayed signal are added to theoutput signal. The different ways ofgenerating these two sound effects are il-lustrated in Figs. 5a and 5b. The soundeffects are rather different also. Strong vi-brato brings to the mind a worn tape re-corder or gramophone with speedregulation problems, while phasing is as-sociated by many with the Hammond -ef-fect based on doppler shift and achievedwith the aid of rotating loudspeakers.

Phasing uses the previously men-tioned comb -filter response that occurs atshort delays (refer back to Fig. 3). Themodulation of the clock signal shifts thepoints of maximum attenuation (poles) ofthe comb filter (Fig. 6) periodically, and socauses a spatial sound effect.

Both vibrato and phasing use delayssmaller than 10 ms, which allows readyuse of a BBD IC.

MN3011/MN3101 BBD chipset

The Type N1N3011 from Panasonic (a Mat-sushita company) contains a 3328 -stagebucket -brigade delay line in PMOS tech-nology. The pin -out and internal configu-ration diagram in Fig. 7 shows that sixtaps on the delay are bonded out to pins.The delay times associated with these pinsare suitable for reverberation applica-tions. The shortest reverberation time isavailable at pin 9, the longest at pin 4. Theactual delay times achieved with the ICare determined by the frequency of theclock signals which are applied in oppo-site phase to pins 2 and 10_ The maximumand minimum delay times at two clockfrequencies, 10 kHz and 100 kHz, aregiven below:

BBD output Delay at Delay at(pin) fa=10 kHz fci-4100 kHz

(ms) (ms)

1(9) 19.8 1.98

2(8) 33.1 3.31

3(7) 59.7 5.97

4(6) 86.3 8.63

5(5) 139.5 13.95

6(4) 166.4 16.64

The operating voltage of the MN3011is 15 V typical and 18 V maximum. At asupply voltage of 15 V, the current con-sumption is 8 mA typical. The direct volt-age at the signal input must be adjustedfor minimum distortion. Starting from alevel of half the supply voltage, a potentialchange of up to 2 V may be necessary. Theamplification of the BBD chip is 0 dB typi-cal (unity gain), but may lie within 4 dB ofthis value. The maximum input level isstated as at 2.5% transient harmonicdistortion (THD). At the nominal inputlevel of 770 mVrrns (1 kHz), the THD is0.4c-, typical.

A bandwidth of 10 kHz is achievable ata clock frequency of 40 kHz. From practi-cal measurements on the chip, the noiselevel is between -70 and -72 dB at a clockof 40 kHz.

The pinning and internal configura-tion of the clock driver chip Type MN3101are given in Fig. 8. External componentsare used to determine the clock oscillatorfrequency, which is divided by two andsubsequently shaped to provide the oppo-site -phase clock signals for the MN3011.The MN3101 has an on -board voltagesource that supplies about 14 /15Vaa. Thisvoltage is required for the BBD chip. Thecurrent consumption of the MN3101 is3 mA typical at 15 V.

The final part of this article will be publishednext month.

Fig. 6. Typical comb filter response of a delay line. The sound effect is 'phasing'.


58

..P.C)111JAI

LETTERS

Letters of a general nature, or ex-pressing an opinion, or concerning amatter of common interest in thefield of electronics (in its widestsense), should be addressed to TheEditor at our London offices. Theirpublication in Elektor Electronics isat the discretion of the Editor.

PRINTED -CIRCUIT BOARDSIn view of the many letters we have had inresponse to my answer in last month'sissue to the letter of Mr Virgis, we have re-considered our position and have decidedon a solution that we feel will please most,if not all, of our readers. As so often, thesolution is so simple that you feel like say-ing to yourself: "why haven't we thoughtof that before?"

Apparently, what I said about it beingimpossible to produce a PCB from the lay-out published in the magazine is not en-tirely true. Accordingly, from this monthon, we will publish not only the compo-nent layout, but also the track side, of all

printed -circuit boards, whether they areavailable ready-made or not. However, thetrack side will be reproduced as a mirrorimage: this will enable anyone to make, orhave made, artwork from which the boardcan be produced.

Because of this change, artwork forPCBs relating to projects published fromthe March 1990 issue onwards can nolonger be supplied. Artwork for boardspertaining to projects published before thismonth will remain available at the termsoutlined in our Readers' Services section.

[Editor]

EUTELSAT TV CHANNELSDear Sir - You mentioned last month(Feb. 1990) that EUTELSAT had switcheda number of its services. Can you tell mewhere I can obtain information on the TVtransmissions from EUTELSAT I?A. Pernfors, Gothenborg.

The information is available from the Eu-ropean Telecommunications Satellite Or-ganization, Tour Maine -Montparnasse, 33Avenue du Maine, 75755 PARIS CEDEX15, France. Details of the TV transmis-sions from EUTELSAT I, F4 and F5, areshown in the tables below. [Ed]

RADIO MAKES A COMEBACKDear Sir - As a rider to your excellent ar-ticle "Radio makes a comeback" (January1990), may I point out that in -car receiverswith RDS are coming down in price. Therecently introduced Sharp in -car radio -cas-sette units, model nos RGF 872 EE andRGF 896E, for example, retail at around£249.00 and £299.00 respectively.M. Young (Young Evett & Young Ltd),London.

Interested readers who are unable to ob-tain brochures on these radios from theirlocal delaer should contact Sharp Elec-tronics (UK) LTd, Thorp Road, NewtonHeath, MANCHESTER M10 9BE, Tele-phone 061-205 2333. [Ed]

UPDATE FOR ATN FILMNETDECODER

Dear Sir -We had been warned by theEditor that the mode of encryption used onthe ATN Filmnet decoder (Elektor Elec-tronics, March 1989) was liable to change.Indeed, the decoder gave an excellent andtrouble -free performance until late De-cember 1989.

When my decoder and that of a friendsimultaneously failed to decode properly,it appeared that the unit was still reinsert -

TELEVISION CHANNELS ON EUTELSAT I - F4, F5

TV F4 (13 degrees East)

TV

Station . Tr Palcarrier(GHz)

Audio(MHz)

Bandwidth(MHz)

Standard Scrant"System Hours Spot

RTL PLUS 1 H 11.007 665 36 PAL Clear 12 WestMIN 3 H 11.174 6.60 36 PAL Clear 9-10 WestTV5 4 H 11472 6.60 36 PAL Clear 9-10 WestWORLDNET 4 H 11.486 6.60 36 PAL Clear 4 WestONE WORLDCHANNEL 4 H 11472 6.60 36 PAL Clear 12 WestGALAVISION 5 H 11.565 665/720 36 PAL Clear 24 AtlantoEUROSPORT 6 H 11.650 6.65 27 PAL Clear 18 WestTELECLUB 7 V 10.986 650 36 PAL Payview 17.5 WestEBC 7 V 10.986 6.50 36 PAL Clear 25 West3SAT 8 V 11.091 6.65 36 PAL Clear 10 EastFILM NET 9 V 11140 6.60 36 PAL Satpak 24 WestSAT1 10 V 11.507 6.65 36 PAL Clear 19 WestSUPERCHANNEL 12 V 11.674 6.65 36 PAL Clear 22 West

ESC (The Euopean BUSeeSS Chorret) is oiso carried on tionsrxxIders I and 6

TVF5 (10 degrees East)

Station Tr Pal TV carrier(Gi-tz)

Audio(MHz)

Bandwidth(MHz) Standard ScrarritAng

system Spot

RAJ UNO 1 H 11.009 6.60 36 PAL Ctar 18 WestWORLDNET 2 H 11055 6.60 36 PAL Clear 4 EastNEINTERNATIONAL 3 H 11149 6.60 36 PAL Clear 24 WestRAI DUE 6 H 11.640 6.60 36 PAL Clear 18 West3SAT 7 V 10.988 6.65 36 PAL Clear 10 WestCANALCOURSES 10 V 11.472 Dgrtat 27 B -MAC Seramb'ed 5 West

ELEKTOR ELECTRONICS NIARCII 1990

READERS' FORUM 59

ing the composite sync pulses correctlyinto the new signal. The line and frameholds were steady, but the picture con-sisted of positive and reversed images,separated slightly and alternating at a slowrate of flicker that seemed to be at half thenormal frame speed, and most irritating towatch.

There are two toggle mechanisms inthe decoder, and it was obvious that nei-ther could cope with the new mode ofslow image reversal. It was a simple pro-cess to suppress one or other image by dis-abling a toggle, but the flicker remained.By studying the circuit description (not forthe faint-hearted) and experimenting withvarious time -constants, I was fortunatelyable to devise a simple by-pass operationthat clocked the bistable at the requiredrate and restored the decoder to its formerperfect function. Remarkably. only one re-sistor and one capacitor are needed asshown in the sketch below.

IC3 poly-pin13 carbonate

IC7

pin10

907061 - 11

A switch was included, in case the pre-vious mode of encryption is resumed inthe future. From the PCB layout it can beseen that IC3 pin 13 is accessible at thethird inter -board link pin from the right,and 1C7 pin 10 is connected to two legs ofP2. so the board need not even be removedfrom its box. The leads to the switch neednot be screened.Dr M. Ball. Chesham Bois.

Thank you for your interest and helpfulsuggestion. The author has replied as fot-

o Ion's: "I have tested your solution on aworking decoder, but found the operationdoubtful and the results poor compared tomy own solution which consists of a sin-gle diode between Q10 of IC9 (a) and R ofFF1 (c). Apparently. your circuit creates atime slot during which the automatic po-larity detector is disabled. The result. how-ever. is a display flicker that was not pre-sent before your modification was fitted.Interestingly, the flicker could be reducedsignificantly (but not sufficiently ) by con-necting the capacitor to IC3 pin 12 insteadof pin 13. In conclusion, I would say thatyour modification is time -critical and itsbeneficial effect may. therefore, differfrom decoder to decoder" [Ed].

SWITCHBOARD

Switchboard allows all PRIVATE READERS ofElektor Electronics one FREE advertisement ofup to 108 characters, including spaces, commas,numerals, etc. per month.

Write the advertisement, which must relateto electronics, in the coupon on this page: itMUST INCLUDE a private telephone numberor name and address: post office boxes are notacceptable.

Elektor Electronics (Publishing) can not ac-cept responsibility for any correspondence ortransaction as a result of a free advertisementor of any inaccuracy in the text of such an ad-vertisement.

Advertisements will be placed in the orderin which they are received.

Elektor Electronics (Publishing) reserve theright to refuse advertisements without givingreasons or without returning them.

FOR SALE. New 3 phase test equipment(no batteries needed): only £5.00. Also. I aminterested in pen friends anywhere in Eu-rope. Amir Sadeg Hashemy, 32 SepidLane, Khayam St, TABRIZ 51736, Iran.

WANTED. Issue no 1634 Vol. 94, Decem-ber 1988 of Electronic & Wireless World. forpayment or exchange for issues 1620 and1624. Verdaguer-Codina Joan, Apt. Cor-reus 37149, 08080 BARCELONA , Spain.

FOR SALE. ILP 1-11/400 240 watt amplifiermodules in goOd working order: £18 eachincl. postage. Phone (0283) 223332 after 6p.m.

FOR SALE. Elektor Electronics May. June.Oct. Dec 1987: March. May 1988: Sept.Nove 1989: 50p each. Phone Steve at10926) 334894.

HOBBY CLEARANCE: all must go! Diskdrives, chips. capacitors and resistors. NorthStar Computer £35; hard disk 80 Mb £125.Send sae for list. Nic Spiers, 20 EatonWay, Gt Totham, MALDON CM9 SEE,Telephone (0621) 892512.

FOR SALE. Southern Instruments oscillo-scope Type \1977: £25 o.n.o. Phone 01-9037172.

WANTED. Software for T199/4A com-puter. or club contact to exchange informa-tion and software. Phone (0524) 39659

WANTED. Manual for Tektronix 4662 plot-ter. Phone Peter at (0604) 767889.

FOR SALE. Westrex and Data -Dynamicsteletypes and one data recording printer witha keyboard and paper feeder. Offers as seen.Phone 021-422 3654.

PEN FRIENDSHIP. I am interested in pen -friends anywhere in Germany with interests

in electronics and digital engineering. Mo-hammed-Etinan-A.T., School of Engi-neering, Shiraz University, SHIRAZ,Iran.

I AM LOOKLNG for students in electronicengineering. preferably final year, to ex-change ideas about projects in transmission.Phone Alex at 01-960 8618.

WANTED. Audio student requires books.test equipment. tools. domestic audio ampli-fier. working or not. Mr. J. Reece, 12 Rail-way Cottages, Station Road, WHIT-STABLE CT5 lAD.

FOR SALE. BBC micro with software costover £500: will sell for £230. Also got DrWho ROM chip in computer. Phone 10222)7703967.

SWAP. Variety of software and games on3.5 in. disk for Amiga 2000. I am also inter-ested in microprocessors Z80. 8086, etc.Hamid Reza Mollahasani, Madjabadi, 30Western 194 St, Tehranpars 16538TEHRAN, Iran. Telephone +98 21783817.

FOR SALE. Linear HF amplifier 2x813G/Grid. 7 bands. 3.5-28 MHz: smart cleanfinish. Sold minus tubes and PSU. £100.Phone (0375) 378783.

HOBBY CLEAROUT. Test equipment.tools, books, shelving. components. Offerson the lot, but may split. Mr. A. Khan, 349St Helens Road. BOLTON BL3 3QD.

WANTED. Working 8052-AH basic com-puter project. Phone (077834) 1137 after6.30 p.m.

Send this coupon to: Elektur Electronics(Publishing). Down House, BroomhillRoad, LONDON SW18 4JQ.

Block capitals please - one character to each box

ELEKTOR ELECTRONICS !MARCH 1990


60

TEMPERATURE COMPENSATION F

LCD MODULES

byAl. Clarkson

Liquid crystal display (LCD) modules have grown in popularityover the past few years because they are easy to use and provide

an attractive display. Unfortunately, they have a troublesomedrawback: poor temperature compensation.This article shows

a way of improving that.

LCD modules come in a variety of sizes:from one line of 16 characters to four linesof 20 characters. They contain all the neces-sary drive circuits, so that interfacing themwith microprocessors is very simple-seeFig. 1.

Unfortunately, the poor temperaturecompensation of these devices makes itnecessary, in order to ensure optimum con-trast of the display, to vary the input signalfrom about 400 mV to 800 mV over thetemperature range 0-50 °C. This signalvariation may, of course, be obtained man-ually with the aid of a simple potentiome-ter, but a much neater way is automatictemperature compensation.

When I started on this problem, Iof all tried the circuit shown inFig.2. This uses a darlington con-figuration to boost the tempera-ture coefficient of the base emit-ter voltage and to reduce the re-quired base bias current.

As the base -emitter voltagedecreases with rising tempera-tures, the current in in R1 drops.This reduces the voltage acrossR,, which in turn increases thevoltage across Re and conse-quently the emitter current. Mostof the emitter current flows inthe collector circuit and thus asthe emitter current increases, thevoltage across R, increases. It fol-lows that the voltage across Rc isdirectly proportional to the tem-perature.

Assuming that the current inR1 and R, is small comparedwith the current in Re, we canshow that the gain of the circuitis related to Ve:

= / R2 = Vb / R,

and

= V, / R, = V, / Re.

In both cases it is assumed that

first

there is no base current.

dVbe / Ri = dit or dithe = dil x Ri,

in which dVbe is the change in base -emittervoltage with temperature.

Now,dVb = dVbe x R, / R1.

Since Vbe is large compared with dI7be,it may be assumed that it is constant, sothat dVb =

dVe/ = (I.= id

dVbe x R, / Rex = di,

dV,=dVbexR,x R, / RIX Re

dV, / dVbe = A = R, x R,/ Rl x Re,

where A is the gain;

R, = Vb / 1; = Vbe/ R, = Vc/i,

and Re = Ve /

Substituting, we obtain:

A = Vb x / x Vbe

Since Vb = - V, - Vbe, this can be re-duced to:

8 EaDala

2:1 0 0. L.

5V

TATCOMPV:SATCJI

O

50:CA'

Fig. 1. Graphical representation of a 4 -digit LCD module.

Fig. 2.

504A

®

16 pA

600-.

3=1

Fig. 3. Fig. 4.

Ve = (V - Vbe) x V, // (Vbe x A +

With this equation we can esti-mate the required Ve and thus theresistor values required.

To calculate the emitter voltagewe need to know the gain re-quired and this is:

A = Tem / Tem,

where Te(R) is the required tem-perature coefficient and Tem isthe temperature coefficient of thetransistor.

Tem of the darlington configu-ration is about 3.2 mV / "C owingto the small collector current (thiscauses a relatively large internalemitter resistance, which reducesthe effective temperature coeffi-cient of the base -emitter junction).

When using the circuit with anLCD module, you must take ac-count of the 27 kS2 internal pull-up resistor-see Fig. 3.

With the Hitachi module , werequire 600 mV at 25 'C. In Fig. 2we see that with a current of500 pA through the transistor andone of 163 j.tA through the inter-nal resistor, the value of R, will be


600 mV / 663 µA = 905 Si A practicalvalue here is 910 Si.

The 27 MI pull-up resistor means thatthe V used in the equation is reduced by

910 / (27,000 + 910) x V = 163 mV.

This makes V = 4.84 V.The Vise of the darlington pair is about

1 V with 500 µA flowing in the collector

circuit, so that

Vbe = (4.84-1)x 0.6 /(1 x 2.5 + 0.6) == 0.743 mV

Let it = 10 µA, so that ie = 510 µA at25 'C. Then:

Re = 0.743 mV / 510 µA = 1.46 kf1;

TEMPERATURE COMPENSATION FOR I.CD MODULES

R1= 1 V / 10 pA = 100 ka

R, = (5 V - 1.743 V) / 10 µA = 325.7 kn.

61

The final circuit is shown in Fig. 4: theoutput from the prototype was linear overthe temperature range of 0-50 'C. At 0 "C,V, = 425 mV and at 50 'C, V, = 850 mV.

SQUARE -WAVE GENERATORby M. Clarkson

Many circuits nowadays require a square -wave generator for whichinvariably a separate NE555 is used. Since many of such circuits

frequently have an unused opamp or voltage comparator available,why not use that to build the square -wave generator?

If the circuit that requires a square -wavegenerator has a spare opamp or voltagecomparator, the diagram in Fig. 1 may beused to realize the generator.

Fig. 1. Basic circuit of proposedsquare -wave generator.

The circuit works by capacitor C beingcharged and discharged to two differentpotentials created by R1, R, and R3. Thetime taken by C to reach the higher poten-tial is the high period of the output, whilethat taken by C to discharge to the lowerpotential is the low period of the output.

To calculate the values of the circuit ele-ments, we must simplify the circuit. Firstly,R1 and R, can be reduced to their Thevenhlequivalent as shown in Fig. 2.

When Vow is low, R3 pulls V, to alower voltage, VT-. Capacitor C is then

R

Vsense

9:0625 - 12

Fig. 2. Thevenin equivalent of R1 and R2.

discharged via R4 to the level of VT-. Whenthe potential across C, V,, reaches VT-, theoutput swings high. WhenVm is high, R3pulls V,n from VT- to VT+. Capacitor Cthen charges via R4. As soon as V, reachesVT+, the output swings low and the cycleis completed.

If a spare opamp is used, the outputfrequency is limited to a range of 10 Hz toabout 10 kHz, but this is sufficient for themajority of applications.

The two states of the circuit, ignoringR4 and C, are shown in Fig. 3. The circuits

(a) (b)

VT

Fig. 3. The two equivalent states of the circuit:(a) ON state (C charges) and (b) OFF state (C

discharges).

in Fig. 3 enable us to calculate VT- andVT+:

VT- = Vs X R3 / (R3 + Rx) [1]

VT+ = (V+ - Vs) x Rx(Rx+ R3) + V,. 12]

So far I have assumed that the opamprequires no bias current-see Fig. 4. This isnot true and, although the current is gener-ally small, it can affect the circuit to quitean extent if R1 and R, are too large. It isnecessary that the current flowing through

R1 and R,, that is, V, / (R1 + R,), is largecompared with the bias current of theopamp.

1 have also assumed that the output ofthe opamp swings between 0 V and V+.However, most opamps have a limitedswing: if the one you use can not swing towithin 10% of the supply voltage, you musttake that into account in the calculations.

T vc

c

(a) (b)

Fig. 4. The two states of R4 and C: (a) ON slate;(b) OFF state.

It, in Fig. 4., we make the difference be-tween VT+ and VT- small compared withV+, we may assume that C is charged anddischarged at constant currents. The time,t, taken by a capacitor to charge at constantcurrent is:

t = dVC / i, [3]

where dV is the voltage C has to charge toand i is the charging current.

The charging current is (V+ -V c) / R4and the discharge current is V, / R4.

If we want C to charge to VT+ and todischarge to VT- in equal times, the charg-ing and discharge currents must be equal,that is,

(V+ - / R4 = V, / R4, 141


62 GENERAL INTEREST

so that

= V+ / 2 [5]

Voltage V, is also equivalent to Vsertse,that is, the mid -point between VT- andVT+.

To recap, I have said that the differencebetween VT- and VT+ must be small com-pared with V+. This allows us to assumethat a constant current flows through C.

Also, V, must be equal to V+/2 to en-sure that C is charged and discharged atthe same rate.

Then, I have assumed that the outputswings between 0 V and V+.

Furthermore, I have not taken into ac-count the output resistance of the opamp.This is all right as long as R3 and R4 aresufficiently large.

Another aspect that must be borne inmind is the common -mode voltage, V, ofthe opamp. As said, V,,ise must be V, / 2,which may be higher than V,m.

Let us now calculate some circuit val-ues: R4 and C may be determined by de-ciding on the frequency, f, and the allow-able charging current, ic: R4 = / 2i, f =1 / T, where T = 2t.

From [3] we obtain

C= / dV.

In terms of frequency,

C=i/ dVx 2f,

Fig. 5. Square -wave generator based on 1 4 TypeLM339 voltage comparator

rent, i, through R1 and R, may be set to25 µA. We then obtain the folowing values:

R1 = V+ / 2i, = 100 1St

R,=R1=100kS2

Since the offset of the LM339 is <5 mV.we may take d V = 200 mV. Then, from 191,

R3 = 1.2 Mil

Assuming we want f = 5 kHz and acharging current, i = 25 µA, then, using[7],we obtain a value for C of 12.5 nF.

The value of R4 is

[61 R4 = / = 50 ka

where dV is the difference between VT+and VT- and this must be small comparedwith V+. At the same time, it must be largecompared with the offset voltage of theopamp. Since the offset voltage is usuallyabout 5 mV, dV should be not less than200 mV. It is calculated by subtracting [1]from [2], which yields:

dV= V+ x R, / (R, + R3). [7]

Since Vse,, =V, = V+ / 2, R1 must beequal to R2, so that R, = R1 / 2. From this itfollows that

When the output of the LM339 is high,the circuit in Fig. 6 may be used to calcu-late the optimum value of the pull-up re-sistor, Rp..11.

Rpuil Ya-Ic

Fig. 6. Simplified circuit to calculate the voltagedV = V+ x R1 / (R1 + 2R). [81 drop across Rpuli.

The value of R3 is then given by

R3 = / 2 (V+ / d V - 1)If we allow a drop of 200 mV across

[9] R ull, and taking into account that

Resistor RI must be small enough to en-sure that the current through R1 and R, islarge compared with the bias current, lb,for the opamp, that is, V+ /2R1 »

Let us now use a quarter of a TypeLM339 voltage comparator as a practicalexample-see Fig. 5. The first thing to noteis its open -collector output, which meansthat a pull-up resistor is required at theoutput. This resistor must be sufficientlysmall not to introduce any errors in ourcalculations.

The V,m of the LM339 is greater than/ 2, assuming that V- = 5 V. The bias

current is around 0.25 µA, so that the cur-

= (V+ - V,) / R3 = 2µA and

= (V+ -Vd / R4 = 50 µA,

we obtain a value for Rpull of

Rpo = 200 mV / + == 200 / 52 = 3.8 ka

In practice, the value may be reducedto, say, 2.2 kfl and even further for low-

impedance loads, but take care as the lowoutput voltage of the I.N1339 may suffer.

Fig. 7. Diagram of the final circuit of a 5 kHzsquarewave generator.

The completed circuit is shown inFig. 7. The prototype under test yielded ahigh period of 94 ps and a low period of96 us. The final frequency was 5263 Hz. Itwas calculated that the capacitor valueshould be 12.5 nF to give a frequency of5208 Hz. Since a 12 nF type was used inthe prototype, the actual frequency wasrather higher, but well within satisfactorytolerance.

Fig. 8. Replacing R4 by a resistor -diode networkas shown enables the mark -to -space ratio of the

output to be altered as required.

The high and low periods, that is, themark -to -space ratio of the output voltage,may be varied by replacing R4 by two re-sistors and two diodes as shown in Fig. 8.1shall leave the derivation to you.


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ISBN 0 905705 28 9Price £8.95

302 CIRCUITSThe popularity of this book is shown by its having been reprinted nofewer than three times. It offers a selection of the most interestingarticles from the 1982, 1983, 1984 summer issues of ElektorElectronics.In it you will find circuits for audio and video; car, cycle, and motor-cycle; home and garden; receivers and aerials; hobbies and games;measuring and testing; oscillators and generators; current sourcesand power supplies; microcomputers and music electronics; and amiscellany of other interesting subjects.

ISBN 0 905705 25 4Price £6.25 net

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WIRE ENDED FUSES 0.25A 3021NEW ULTRASONIC TRANSDUCERS 40kHz Moan'12 CORE CABLE 70.2mm OVERALL SCREEN £11 metresPOWERFUL SMALL CYLINDRICAL MAGNETS 311OP AMP LM10CLN £2.90BNC 50 OHM SCREENED CHASSIS SOCKET 3 21BNC TO CROC CLIPS LEAD 1 metre £1MAINS ADAPTOR 9V DC 200m £1.25MOULDED INDUCTOR 470..size of a I watt film resistc r ...... .... sr'TO -220 HEAT SINK sim RS 4: -3- 82 _...14.1250

£1 each

SMALL MICROWAVE DIODES AEI 0C1026A 2.11D.I.L SWITCHES 10 WAY £1 8 WAY 80p 4676 WAY 80p180 volt 1 watt ZENERS also 12V & 75V 2021PLASTIC EQUIPMENT CASE 9x6x125 WITH FRONT ANDREAR PANELS CONTAINING PCB WITH EPROM 2764-30AND ICS 7417 L530 LS32 LS367 7805 REG. 9 WAY CI PLYG.PUSH BUTTON SWITCH. DIN SOCKET £1.90VN I OLM 60v.A 50hrn TO -92 mosfet 411 100120MIN GLASS NEONS latlRELAY 5v 2 pole changeover looks Wce RS 355.741 markedSTC 47WBost £1 eaMINIATURE CO -AX FREE PLUG RS 456-071 . 2E1MINIATURE CO -AX FREE SICT RS 456273 .211.50DIL REED RELAY 2 POLE No CONTACTS ElPCB WITH 21/2646 UNUUNCTION with 12v 4 POLE RELAY

£1400m 0.5W thick film resistors (yes tour hundred megottrris)

4,21STRAIN GAUGES 40 ohm Foil type polyester backed balcogrid alloy .£1.50ea 10-£1ELECTRET MICROPHONE INSERT £0.90linear Hall effect IC Moro Switch no 613 5S4 sun RS 304257

£2.50 100,£1.50HALL EFFECT IC UGS3040 + magnet £1OSCILLOSCOPE PROBE SWITCHED xl x10 _._______ £10CHEAP PHONO PLUGS . 100.12 10001101 pole 12 way rotary switch 411AUDIO ICS U.4380 LM386. El ea555 TIMER S'El 741 OP AMP 621ZN414 AM RADIO CHIP . 80pCOAX PLUGS nice ones 4 21COAX BACK TO BACK JOINERS 3 214x4 MEMBRANE KEYBOARD £1.5015.000uF 40V U-50(£1.25)INDUCTOR 20uH 1.5A ..... ... __________ 5.11NEW BT PLUG - LEAD £1.50125' PANEL FUSEHOLDERS 3E1CHROMED STEEL HINGES 14.5x1" OPEN £1 each12v 1.2w small wire ended lamps fit AUDI VW SAABVOLVO 1011STEREO CASSETTE HEADMONO CASS.HEAD £1 ERASE HEAD 50pTHERMAL CUT OUTS 50 77 85 120"C El eaTERMAL FUSE12IIC 241W 15A 5E1TRANSISTOR MOUNTING PADS TO-STO-18 ..... £31000TO -3 TRANSISTOR COVERSSTICK ON CABINET FEET .PCB PINS FIT 0.1' VERO 20011TO -no mites - d_mhes _________TO -3 ma bushes _PTFE min screened cable .....................Large heat shrink sleeving pack £2CERAMIC FILTERS 6M.,90.1/10.7M . 60p 100E20MAINS LEAD WITH MOULDED 13A PLUGSOCKET ...... £1.50IEC chases plug filter 10A £3Potentiomenters short spindles values 2k5 10k 25k 1m20.15 flri 411500k lin 500k log

.

_. 41140khz ULTRASONIC TRANSDUCERS EX-EOPT NO DATA

£1,0PLESSEY INVERTER TRANSFOFIMER 80 CYCLES11 5.0.11 5V to 240., 200VA £6(£3)

DIODES AND RECTIFIERS1N4148 ...... . .

1N4004,SD4 1 A 300V1N5401 3A 100VBA158 IA 400V fast recoveryBA159 to 1000V fast recovery120V 35A STUDBY127 1200V1.2ABY254 800V 3A ......... . . .

BY255 1300V 3a ...._EA 100V SIMILAR MR751IA 6430V BRIDGE RECTIFIER4A 100V BRIDGE6A 100V BRIDGE8A 200V BRIDGE10A 200V BRIDGE25A 200V BRIDGE £225A 4C :IV BRIDGE £2.50

10.E1_ 3021

10.50p loam15£1

10021.50100E310E1

100£3100c4

65p_El=E1

£1

4 El4 £13 £12£1

...... 211.35£1.50

10/1810E22

SCRSPULSE TRANSFORMERS 1.1.4 £1.252P41.1EQUIV C106D 3 £1MCR72-6 10A 600V SCR _ ..... ... £135A 800V STUD SCR £2TICV106D 800mA 400V SCR 311 .....--- 100 215MEU21 PROG. UNUUNCTION £1

TRIACS DIACS 4/£1B1137.800 8A TO -220 2 £1BT138-600 12A TO -220 70pNEC TRIAC ACO8F BA 600V 10220 . E2 100 230TXAL225 8A 400V 5mA GATE 2E1 102135TRAL223013 30A 400V ISOLATED STUD MathCONNECTORSD25 IDC SOCKET FUJITSU34 ...ay card edge IDCCONNECTOR (disk drive type) .. £1.25

Kov-rFicDNIcsTEL. 0279-505543FAX. 0279-757656

P 0 BOX 634BISHOPS STORTFORD

HERTFORDSHIRE CM23 2RX

CENTRONICS 36 WAY IDC PLUG £2.50CENTRONICS 36 WAY IDC SKT ................ 24330BBC TO CENTRONICS PRINTER LEAD 1.5M ...... £3.50CENTRONICS 35 WAY PLUG SOLDER TYPE £4USED CENTRONICS 35W PLUG . SKT . £3

USED D CONNECTORS price per pairD9 60p D15 21.50.1325 £2. D3712. D50 £3.50 covers50p ea

WIRE WOUND RESISTORSW21 or sm 2.5W 10 of one valueR10 OR150R21 2R04R7 5R0 5R2 = 2 rz 2 re; 15R18R 2OR 22R 27R 33R 47R 56R 62R 9 t R 1208 1130R390R 430R 470R 6130R 820R 9108 1105 1K2 11(5 1K82K4 21(7 3K3 31(0 5K0 RO5 (50 'men -ohm) 1% 3W 4 for £1W22 or sun 6W 7 OF ONE VALUE ___ _ £1R47 R52 1R0 1R5 1R8 3R3 6R8 9R1 I2R 20R 24R 27R33R 51R 55R 62R 68R 100R 1213R MR 226R 393RSSOR 620R 910R 1K0 1K2 1K5 1K8 2K2 21C7 3K3 3K94K7 8K2 10K 151C 16K 20KW23 or sin 9W 6 of one value -..._...__-----_..-._ -_£1Ft22 R47 1R0 1Rt IRA 56R 62R 100R 120R 180R 220R300R 399R 650R I KO 1105 5K1 10KW24 or Sim 12W 4 OF ONE VALUE £1R50 2R0 9R1 18R 22R 27R 56R 66R 75R 62R IDOR150R 18.0R 200R 220R 270R 400R 620R 1K0 6K8 8K210K 15K

PHOTO DEVICESSLOTTED OPTO-F., .'. ITCH OPCOA OPB815 £1.302N5777 50pTIL81 PHOTO TRANSISTOR £1TIL38 INFRA RED LED 5E14N25. 0P12252 OPTO ISOLATOR _-_____ 503pPHOTO DIODE SOP 612MEL12 (PHOTO DARLINTON BASE nic) 50pLED's RED 3 or 5mm 12/1 . 10016LEDs GREEN OR YELLOW 10 -21..-..-. 100£6.50LEDs ASSORTED RD GWYW - INFRA RED _..._200E5FLASHING RED OR GREEN LED 5mm 50p .-. 100E40

STC NTC BEAD THERMISTORSG22 220R. G13 1K, G23 21, G24 20K. G54 50K. 025200K. G16 1M. RES 20"C DIRECTLY HEATED TYPE £1esFS22BW NTC BEAD INSIDE END OF GLASS PROBERES 2010 200R £1 eaA13 DIRECTLY HEATED BEAD THERMISTOR 1k res.ideal for audio Wien .-----------------.- £2 ea

CERMET MULTI TURN PRESETS ."lOR 20R 10OR 200R 250R 500R 2K 2K2 21(5 5K 10K47K 501C 100K 200K 500K 2MK 50p ea

IC SOCKETS6 pin 15.21 8pin 12E1 14/16pin 1011 1820 on 711.2224/28 ph 411 40 30p

SOLID STATE RELAYS40A 250V AC SOLID STATE RELAYS El 0

POLYESTEFt/POLYCARB CAPS- 220n 63v 5-- 20 El 100E3

= n3 -71 100E510:15n22n.33n.47r..22.-.. 10-nm rad 10013.50100n 250v radar --_-__----..100 23100n 600v Sprague axial 10E1 101116(£1)2u2 160v rad 22rnm.2u2 100v red 15rnm 1032101 Ori33n.47n 250v ac x rated 15mm 10 21470n 250v ac x rated rad 4 £11U 600V MIXED DIELECTRIC 50p eala) 100v rad 15nun, 1u0 22rnm rad C3 £6

RF BITSMINIATURE CO -AX 50 OHMs URM95 El 2TRIMMER CAPS ALL 4 50pSMALL 50 2 p.71 mounting 5mm centresSMALL MULLARD 2 to 22pF 4 SOpSMALL MULLARD 5 to 50pF _ 4 50pLarger type grey 2 to 25pF black 15 to 200TRANSISTORS 2N4427 60pFEED THRU CERAMIC CAPS 100pF _ 10 21

MINIATURE RELAYS &Male for RF5 volt coil 1 We changeover £1

5 volt coil 2 pate changeover £1

12 ..,o'tcc.11 odle cnangadv4.

MONOLITHIC CERAMIC CAPICITORS10n 50e 2.5mm 10-3 £4.50100n 50v 2.5mm or 5mm 100 26100n ax short leads . 100 E3100n ax lorg leads .100E5100n dac.kage - . 100 28

STEPPER MOTORS4 PHASE TWO 9V WINDINGS £3.50

MAIL ORDER ONLYMIN CASH ORDER £3.00 OFFICIAL ORDERS WELCOME

UNIVERSITIES COLLEGES SCHOOLS GOVT. DEPARTMENTSMIN. ACCOUNT ORDER £10.00

P&P AS SHOWN IN BRACKETS (HEAVY) ITEMS65p OTHERWISE (LIGHT) ITEMS

ADD 15% VAT TO TOTALELECTRONIC COMPONENTS

BOUGHT FOR CASH

VISA


Dollble TopsDUAL BAND VHF (45INFUHF (35W) ALM MOBILE TRANSCEIVER

When only the best la good enough-and it still want somethin better

Cross Band Full Duplex4 Scanning Modes10 Function Memory Channels

* Highly Visible Colour LCD Display* Illuminated Front Panel Controls* 5 Channel Spacing Steps* Duplexer

Function Keys have UniqueAudible ToneBell FunctionCompact & Lightweight

Accessories Included:* Hand-held microphone* Mobile mounting bracket* Mounting hardware* Power cable

ALINCOfrom MAPLINthe authorised

) distributor

'-ANItvieuromemeiliaitisiormistr_

This very high quality 2m7Ocm FM dual band mobile transceiver has beenspecialty designed to provide maximum performance and operatingconvenience in an ultra compact package. An impressive array of featuresgives maximum flexibility in mobile installations. The transceiver has anoutput power of 45W (VHF) 35W (UHF) and incorporates a high low powerswitch. The unit is provided with 10 programmable memories. Channelspacing is in 5. 10. 12.5. 20 and 25kHz steps. There are four scanningmodes:

1. VFO scanning of the entire band. 2. Memory scanning of selectedmemories. 3. Programmed band scanning of a selected segment ofthe band. 4. Priority scanning allows selection of a frequency, in VFOor memory, to serve as a priority frequency.

A duplexer is built-in so that when an antenna for both bards is in use.only one feeder cable for the transceiver is necessary.

The unit is supplied with a comprehensive instruction manual. It isillegal to transmit with this unlur!ess you bolt a Ratio Amateur sClass B (or A) licence.Quote Reference DBT4 0 2499.95

Ultra compact. lightweight design6.5W Output Power(with optional 12V battery pack)Simple OperationEasy to See LCD Display10 Channel MemoriesBattery SaveFunction LockTone Burst

- Amazing Compact Size Only 3x6x 17 cm approx.

A very high quality, lightweight, 2m handheldtransceiver, incorporating many useful features.This transceiver is extremely simple to operate.most functions can be performed with one hand!

Quote Reference AtiTtiO £219.9512V Ni-Cad Battery Pack

For use DIM giber atere horMed trarsreirersA 12V 700oM Way pack kith reagrel DC -DC clxklerterwtidt alms tie transceiver bo be powered lTan a mr

cigarette ighter Kciat.A cArger is &o eratehe kr roe *V; =

Batter' Pa.NBP40 t59.95 Charger IISC4O

L15.000 '13 3 0 0 0pfip ; ;;; 00000 illn

/,nn000 muslinsav P. IPMIP,

MEN

1Wift -BAND .SUB

(1R -5-713xMP/

MOP,11111!

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61V VHF 5W UHF Output Power(with optional 12V battery pack)Cross Band Full Duplex Operation

* Frequency selection by DirectKeyboard Entry or Step Up Step Down

* Automatic Battery Save Function* 20 Memory Channels* Built-in DTMF Keypad and Encoder* Amazing Compact Size Only

32.: 6 19 cm approx.

This unit is very compact and is one of the smallestdual band transceivers currently available. Withthe battery pack supplied output power is 2.5W forVHF and 2W for UHF. Frequency selection iseither by direct keypad entry of the requiredfrequency or by using step up step down buttons inincrements decrements of 5kHz. 100kHz and1MHz. An automatic battery save (ABS) functionwill extend battery life considerably. There are 20memories (10 VHF and 10 UHF) for storingoperating, offset and tone frequencies. Thescanning facility has a priority function which hasthe ability to scan between chosen VHF and UHFfrequencies. A 10dB RF attenuator is switchselectable and can be used in areas of high RFsaturation.

Quote Reference DliT40 £369.95

ELECTROVCS_

P.O. Box 3, Rayleigh, Essex SS6 8LR.

CREE)911" CANE IMOVP

0702 554111=111911 Ar.terorAn

E-llaseess ViS4

PHONE BEFORE 5PM FOR SAME DAY DESPATCHa cal in at a - Seigoi.. Le Kain'765n-M. Edair&e, lia-cestet. !icccrgra7.

Heating. Sa..1raldr..n and Scccrend-on-SeaAdd 7:-.13 Eon mrCage on at rnal Orders. Uwe/ enia-rg a cP.i-9 add 5C canna

Soiled x xrakOjay. Pigs rrs,y crave ate.' May 1st 1993.

SEE THE COMPLETE RANGE OF TRANSCEIVERS Allin LOTS MORE IN OUR BUMPER 580 -PAGE CATALOGUE

ON GALE NOW AT ALL BR HITCHES OF WHSMITH -PRICE £2.25!

surge plug pause switch for camcorders...post code return to technomatic ltd. techno house. l468...

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